Heavily Modified Water Bodies Research Articles

Assessing the ecological potential of reservoirs: a principal response curve (PRC) analysis approach

Heavily modified water bodies (HMWB) have been seriously affected by human activities and natural processes promoting their imbalance, and impacting their functioning and biodiversity. This study explores a new approach of monitoring and assessing water quality in Mediterranean reservoirs using phytoplankton communities across a disturbance gradient, according to water framework directive. Phytoplankton and environmental data were sampled in 34 reservoirs over 8 years. Two types of reservoirs were analyzed: Type1 “run-of-river reservoirs” (located in the main rivers, with a low residence time); and Type2 “true reservoirs” (located in tributaries, with high residence time). The transition from deeper and colder reservoirs (reference sites) to shallow and warmer (impaired sites) was clear in Type2, correlated to organic pollution and mineral gradients. Impaired sites from both types showed a higher richness of tolerant taxa. Principal response curve (PRC) provided a concise summary of phytoplankton temporal dynamics and assessed ecosystem health for Mediterranean HMWBs. PRC will provide a powerful tool for environmental quality assessment and be incorporated into monitoring and assessment programs. This approach can help policymakers to manage natural capital to achieve multiple objectives, mainly increasing ecosystem services, and improve readability and interpretation of spatial patterns in temporal changes.

Methodological Framework for Assessing Hydromorphological Conditions of Heavily Modified and Artificial River Water Bodies in Croatia

Water Framework Directive (WFD) guidance documents from 2019 provide a comprehensive review of methods and guidelines to improve the comparability of heavily modified water bodies (HMWBs) in the European Union. However, there is currently no common, single methodology for monitoring HMWBs and artificial water bodies (AWBs) or for determining maximum (MEP) and good ecological potential (GEP). This study presents the first assessment of hydromorphological conditions of HMWBs and AWBs in Croatia based on type-specific indicators. The typology of HMWBs and AWBs was based on distinct hydromorphological characteristics and modifications in order to be easily related to the uses of the water bodies. The classes of hydromorphological potential were graded from the theoretical MEP, which was determined by the score scale as the tolerated deviation from natural reference conditions, considering potential mitigation measures. The use of the water body and/or the effects on the wider environment were considered while determining MEP and choosing indicators included in monitoring and assessment. In the case of AWBs, the parameters dependent on natural reference conditions, which are non-existent, were omitted from the assessment. Only 27% of HMWBs and 2 out of 51 AWBs achieved good potential for all three hydromorphological elements. The most significant hydromorphological modifications include channelization, straightening, deepening and removal of riparian vegetation due to flood-protection management practices. In order to achieve the environmental objectives set out by the WFD, the Croatian water management system has to start implementing mitigation measures, especially related to natural flood management.

Contribution of a groundwater-influenced hinterland drainage system to the restoration of salmonid spawning grounds at the upper river Danube

Groundwater-influenced ditches, so called hinterland drainage systems (HDS), accompany many heavily modified water bodies (HMWBs). Herein, we evaluate the usefulness of including HDS as functional habitats in river restoration approaches by assessing their role as salmonid recruitment areas in HMWBs. We tested the functionality of spawning grounds in a groundwater-influenced HDS compared to the quality of those not influenced by groundwater (OHB 1 and OHB 2), based on bioindication using brown trout eggs. Eggs were placed in each compartment of a two-layered container of 20 cm diameter and 30 cm total depth (known as the HydroEcoSedimentary Tool or HEST) pre-filled with sediment, mimicking hyporheic conditions. A total of 81 HESTs were evenly distributed across the three sites to assess egg and larvae mortality whilst exposed at two substrate depths (5–10 cm and 17–22 cm). In addition, key physico-chemical variables such as dissolved oxygen, temperature, pH, turbidity, electric conductance and substratum composition were analyzed. Mean egg mortality in the HDS was 33% lower than in both non-groundwater-influenced spawning grounds, whereas mean larval mortality was highest in the HDS (95%) compared to 74% at OHB 1 and 66% at OHB 2. The exposure depth of eggs had a significant influence on mortality, with more dead eggs and larvae in the deeper substrate layers, most likely attributed to an increase of fine sediment and a decrease of oxygen availability over time. Particularly the HDS revealed high mortality rates of larvae since it had a 17% lower mean oxygen level compared to the other spawning grounds. These findings suggest that if additional measures such as substratum restoration were undertaken to increase oxygen availability within HDS, these groundwater-dominated ditches could be incorporated as part of an efficient river restoration strategy.

Flora and plant communities across a complex network of heavily modified water bodies: geographical patterns, land use and hydrochemical drivers in a temperate overexploited plain

The decline of freshwater flora due to alteration, reclamation and trophic perturbation of lowland wetlands is among the most relevant issues in biological conservation. The contribution of heavily modified water bodies (HMWBs) in preserving plant diversity is notable, but the underlying ecological mechanisms are not completely explored. To contribute to this debate and expand the knowledge on the role of HMWBs in maintaining wetland biodiversity in overexploited agroecosystems, a canal network of about 1150 km (SE Po valley, N-Italy) was analysed to study the geographical patterns of riparian flora and plant communities, and their land use and hydrochemical drivers. A systematic sampling procedure was adopted by randomly selecting 96 transects (10 m2) along 79 drainage canals. Additionally, 22 transects were sampled for water quality evaluation. Flora was characterised based on species richness and presence of threatened, alien and invasive species. We also studied the contribution of land use and water quality in explaining plant richness and composition. Slope and aspect of canals do not significantly affect plant species composition, whereas the «proximity to protected areas» seems to have a negative influence. Both threatened and alien plants richness decrease approaching protected areas. Among land use types, only agro-zootechnical settlements influence plant species composition, favoring nitrophilous species, as demonstrated by water parameters (the spatial patterns of nitrophilous species mirrored the progressive worsening of canal waters). This work confirms the key role of HMWBs in sustaining plant species diversity in oversimplified landscapes, highlighting complex regulation mechanisms that need further investigations.

Selection of an indicator to assess a highly modified saline ecosystem

The Water Framework Directive (WFD, 2000/60/EC) determines that all water bodies must achieve a good ecological status. The solar salterns system of Mata-Torrevieja (Spain) has been designated as Heavily Modified Water Bodies (HMWB). This ecosystem is a transitional water body (TW) largely conditioned by socio-economic management plan and the related human activities that take place. Thus, WFD establishes as obligatory the determination of their ecological potential, and not their ecological status. In order to define the ecological potential, it is necessary to determine previously the chemical and biological conditions of the water body. This paper is focused on the analysis of physical-chemical parameters of a saltern system during 2008–2016, in order to establish a starting point for the implementation process of the WFD in this type of ecosystem (TW-HMWB). The behavior of salinity and physical-chemical parameters (temperature, pH, nutrients) has been studied. Salinity was the most relevant parameter studied to define pressures for these water bodies. However, total phosphorus turned out to be a good potential status indicator. It would be one of the most suitable chemical parameters to propose a methodology for the determination of the ecological potential in the salterns.

Defining Maximum Ecological Potential for heavily modified lowland streams of Northern Italy

In relation to hydromorphological alteration the Water Framework Directive (WFD), a major piece of European legislation, has introduced the concept of Heavily Modified Water Bodies (HMWB). In water bodies falling in this category, hydromorphological modifications are permanent, significantly alter the character of the river and cannot be removed without compromising the use of the water body. In HMWBs a dedicated approach to the evaluation of their status is set, and their Ecological Potential must be assessed. Crucial to the process is the definition of Maximum Ecological Potential (MEP) as the reference conditions for HMWB. In the present paper we aim to define MEP conditions for Italian heavily modified lowland rivers, affected by strong bank protection (i.e. levees or bank reinforcement) in reason of flood protection and land drainage uses. The approach applied to identify MEP conditions follows the one considered for natural (not heavily modified) rivers in Italy and large part of Europe and bases on the identification of ‘reference sites’ representative for the river category and alteration. For the selection of MEP sites environmental features representing mitigation measures and/or expected natural features were considered. The ability of such features in discriminating MEP and disturbed sites was verified by multivariate analyses run on abiotic features (Principal Component Analysis) and biological communities (non-metric multidimensional scaling). We demonstrated differences both in terms of invertebrate community and biological metrics used to assess ecological status (and potential) between MEP and impaired river stretches. Finally, we recognized relevant habitat features able to clearly separate MEP reaches from nonMEP reaches with indication on the type and quantity of measures significant for benthic invertebrates and applicable in lowland Heavily Modified Water Bodies.

Reflectance spectra classification for the rapid assessment of water ecological quality in Mediterranean ports

Summary Ports are open systems with direct connection to the sea, therefore any potential impact on port waters may have implications for the health of adjacent marine ecosystems. European WFD addressed ports in the category of Heavily Modified Water Bodies (HMWBs) and promoted implementation of protocols to monitor and improve their ecological status. TRIX index, which incorporates the main variables involved in the trophism of marine ecosystems (Nitrogen, Phosphorus, Chlorophyll a, Dissolved Oxygen), is widely utilized in European coastal areas to evaluate trophic status. The relationships between the variables involved in TRIX computation, particularly Chlorophyll a concentration, and water spectral reflectance provides an alternative method to evaluate the quality and ecological status of the port water. Hyperspectral (380–710 nm) water reflectance data were recorded by a portable radiometric system in five ports from the Western and Eastern Mediterranean Basin. The spectral distance between samples was measured by two metrics using both the original and reduced spectra and was implemented within a hierarchical clustering algorithm. The four spectral classes that emerged from this operation were statistically analysed versus standard water quality descriptors and phytoplankton community features to evaluate the ecological significance of the information obtained. The results indicated a substantial coherence of different indicators with more than 60% of the total TRIX variability is accounted for by the proposed classification of reflectance spectra. This classification is therefore proposed as a promising Rapid Assessment Technique of ports water ecological quality, which can serve as an effective monitoring tool for sustainable management of ports.

Structural Floating Wetlands: Achieving Ecosystem Services in Heavily Modified Waterbodies

Floating ecosystems are now being employed in waters and along waterways around the globe. They provide “natural ecosystems” in these heavily modified environments. They beautify urban shorelines, help improve water quality, all while providing habitat for fish, birds, and other wildlife.

A multi-approach Lake Habitat Survey method for impact assessment in two heavily modified lakes: a case of two Northern Greek lakes.

Despite hydromorphological pressure assessment is required by the European Water Framework Directive (WFD), there is not one commonly accepted method for this purpose. The extent of habitat alteration and naturalness loss is a major issue especially for heavily modified water bodies (HMWBs) in terms of their maximum ecological potential designation. In this research, a broadly used methodology in Central and Northern Europe, Lake Habitat Survey (LHS), is tested for the first time in Greece in two natural urban shallow lakes to estimate the extent of habitat modification and hydromorphological alteration. The LHS methodology was deployed using three different approaches (on foot, by boat, and remotely by satellite sensing), by two observers, to assess simultaneously the method's reproducibility and subjectivity and selecting the best approach. All three LHS deriving indices (Lake Habitat Quality Assessment-LHQA, Lake Habitat Modification Score-LHMS, and Alteration of Lake Morphology Scores-ALMS) for each approach and each observer were calculated. Both lakes were described as substantially changed in character, receiving multiple pressures and hosting habitats of impaired quality and degraded shores. The research revealed low level of consistency among the approaches but highlighted the method's objectivity since no statistically significant differences were found on indices between the two observers. LHS proved to be an easily applicable, useful tool for hydromorphological assessment in these two case studies and could be further applied as a WFD screening tool.

Is it Worth the Money? The Functionality of Engineered Shallow Stream Banks as Habitat for Juvenile Fishes in Heavily Modified Water Bodies

AbstractHeavily modified water bodies (HMWB) are characterized by monotonous and straightened channel morphologies with high degrees of bank enforcement. They often lack shallow bank habitats, which are considered important for critical life stages of fishes. In this study, three principle options to engineer shallow stream zones were assessed concerning the value of the created habitats for larval, juvenile and adult stages of fishes in 30 sites from three HMWB. The construction scheme of the juvenile habitats comprised different degrees of embankment ranging from rip‐rap structures with steep bank angles to almost nature‐like construction schemes with very flat river‐banks and sparing usage of structural enrichment such as boulders and dead wood. In general, the differences between the three habitat types were more pronounced in density of different life stages than in the presence or absence of species or certain life stages. A steep bank angle and a high degree of engineering such as placement of rip‐rap embankment, boulders or dead wood structure in the habitats were hardly accepted by early larval and juvenile stages of rheophilic fishes. In contrast, the construction scheme of a nature‐like habitat with a flat bank angle (<10%), low water depth (mean = 24 cm) and a sparing usage of coarse woody debris (CWD) and boulders had the highest success. Other investigated habitat types did not provide additional benefit, neither in terms of supporting additional species and life stages, nor in high individual numbers and should thus only be implemented when land for restoration is scarce and nature‐like habitats cannot be realized. Copyright © 2016 John Wiley & Sons, Ltd.

Transport time scales as physical descriptors to characterize heavily modified water bodies near ports in coastal zones

Physical descriptors that characterize Heavily Modified Water Bodies (HMWB) based on the presence of ports should assess the degree of water exchange. The main goal of this study is to determine the optimal procedure for estimating Transport Time Scales (TTS) as physical descriptors in order to characterize and manage HMWB near ports in coastal zones. Flushing Time (FT) and Residence Time (RT), using different approaches—analytical and exponential function methods—and different hydrodynamic scenarios, were computed using numerical models. El Musel (Port of Gijon) was selected to test different transport time scales (FT and RT), methods (analytical and exponential function methods) and hydrodynamic conditions (wind and tidal forcings). FT, estimated by the exponential function method while taking into account a real tidal wave and a mean annual regime of wind as hydrodynamic forcing, was determined to be the optimal physical descriptor to characterize HMWB.

A pragmatic approach to define the ecological potential of water bodies heavily modified by the presence of ports

Abstract Due to the great number of ports along the European coast, defining the ecological potential of heavily modified water bodies (HMWBs) by the presence of ports is crucial in the development of river management plans. Numerous approaches have dealt with the assessment of the ecological status of natural water bodies, but there are few which specifically cover HMWBs. This contribution proposes pragmatic approaches to define the ecological potential of port areas. Besides being coherent with the hydromorphological alterations, the methodologies developed ensure the functioning of the ecosystem while recognizing that the communities and conditions found in HMWBs are highly determined by the major hazards associated to port activities. The main output is a versatile site-specific approach able to identify the best possible indicators and reference conditions (maximum ecological potential; MEP) to evaluate the ecological potential in port areas. The implementation at the port of Santander stressed the importance of considering water, sediments and biological indicators to evaluate the ecological potential, confirming sediments as the main testimony of the contaminant episodes.

Searching for a compromise between ecological quality targets, and social and ecosystem costs for heavily modified water bodies (HMWBs): the Lambro-Seveso-Olona system case study

The Lambro-Seveso-Olona (L-S-O) system derives from the human regulation of the natural hydrology of the territory around Milan city area. The average population density in the L-S-O area is among the highest in Italy and Europe. Industry is also highly developed in this basin: chemical, textile, paper, pulp and food industries being the most important ones. Although, at present, the L-S-O system no longer receives the untreated wastewaters of the Milan urban area, treated wastewaters constitute about half of the streamflow. Biotic communities in this river have a long history of poor quality status, having suffered great damage due to domestic and industrial discharges. Recently, new chemical quality standards for macropollutants have been set by the Italian legislation as support for the good ecological status according to the Water Framework Directive (WFD). This new index is very restrictive, and it makes it extremely challenging to achieve the water quality objectives for the L-S-O system. The aim of this study is to analyse through a modelling exercise the restoration possibilities of the L-S-O system, investigating both the source apportionment of the macropollutants, the discharge limits that should be set to achieve the good quality status and their corresponding cost.

Setting the maximum ecological potential of benthic communities, to assess ecological status, in heavily morphologically-modified estuarine water bodies

Investigations on setting benthic macroinvertebrates reference conditions in natural waters have increased recently. Under the European Water Framework Directive, importance is given to research in morphological heavily-modified water bodies (HMWBs), which are very common in countries with high human pressure. However, research has not been undertaken on setting the maximum ecological potential (MEP), as a reference in HMWB. The objective of the present investigation is to set the MEP of two metrics (diversity and richness), used in assessing the ecological status in different benthic indices. The Oiartzun estuary (Basque Country) is used as a case study, which changed morphologically in the 19th Century, following harbour construction. Data obtained from 1874 and the present were used to model changes in currents, water residence time, salinity, volume, and intertidal area. Benthic macroinvertebrate data, from 1995 to 2011, were used to predict 19th Century and present MEP. Changes in the estuary were described: loss of all of the intertidal areas; doubling of the volume; residence time, changing from 2 to 95days; current velocity reduced by 50%; salinity increase. All these factors have led to changes in the benthic communities and the structural variables. Predicted richness and diversity, for 1874, were lower (48–76%) than those at present. Taking into account the differences between natural and modified waters, it is proposed to utilize 75% of the natural reference conditions, as the MEP values for Basque HMWB.

Pressures at larger spatial scales strongly influence the ecological status of heavily modified river water bodies in Germany

River biota are influenced by anthropogenic pressures that operate at different spatial scales. Understanding which pressures at which spatial scales affect biota is essential to manage and restore degraded rivers. In Europe, many river reaches were designated as Heavily Modified Water Bodies (HMWB) according to the European Water Framework Directive (WFD), where the ecological potential might mainly be determined by pressures at larger spatial scales outside the HMWB (e.g. hydromorphological alterations at the river network and land use at the catchment scale). In Germany, hydromorphological alterations and diffuse pollution were the main pressures. Therefore, the three objectives of this study were to (i) identify the hydromorphological pressures at the site, reach, and river network scale, and land use categories at the catchment scale which significantly affect the ecological status of HMWB in Germany, (ii) quantify the relative importance of these pressures at different spatial scales, and (iii) analyse the differences in response between fish and macroinvertebrates. The results indicated that: (i) At the reach scale, fish were most strongly influenced by channel-bank conditions whilst the naturalness of channel-planform was the best proxy for the ecological status of macroinvertebrates. At the catchment scale, urbanization was the most detrimental land use. (ii) The pressures at larger spatial scales (catchment land use and hydromorphological alterations in the river network) generally were more important than hydromorphological alterations at the reach scale. (iii) Fish were affected equally by both, hydromorphological alterations at the reach scale and large-scale pressures whereas the latter were far more important for the ecological status of macroinvertebrates. In conclusion, these results indicated that large-scale pressures may often limit the efficiency of reach-scale restoration, especially for macroinvertebrates, even in the absence of saprobic pollution, and have to be considered for the management and restoration of HMWB in Germany and comparable degraded river reaches.

Flushing time as a descriptor for heavily modified water bodies classification and management: Application to the Huelva Harbour

Since the flushing time is a physical descriptor used to distinguish between different types of heavily modified water bodies (HMWB), the establishment of a methodology for its calculation becomes important. In order to achieve this task, a methodological procedure involving the tide mean value and variable river flow values is proposed. The hydrodynamics were assessed using a two-dimensional model which integrates the depth-averaged mass and momentum equations in the time and space domains and includes a wet-dry point treatment method. The hydrodynamic model calibration and validation were performed on the basis of tidal gauge and velocity current measurements. A reasonable agreement with the field measurements of water elevation and velocity were achieved. On the other hand, a two-dimensional mathematical model, which solves the depth-averaged advection-diffusion equation, was properly calibrated and used to evaluate the behaviour of a conservative tracer within a water body. The transport model calibration was developed according to the field survey data carried out during late spring when the rivers flows are low. This study allowed the flushing time estimation under four scenarios showing that only the estuarine mouth presents a high renewal rate because the current velocities are higher. For heavy rain periods, a flushing time decrease was observed as river flows modify the circulation in the main channel. Neglecting the river forcing was found to be valid for the dry period.

Ecological status assessment of the rivers in Slovenia – an overview

Adoption of the Water Framework Directive (Directive 2000/60/EC) includes ecological assessment of water bodies with biological communities. A WFD compliant ecological assessment includes ecological typology of water bodies, definition of reference conditions and classification system with five ecological classes. In this paper, an overview is given on the development of the ecological assessment system for Slovenian rivers. A special emphasis is laid on ecological river typology. 74 ecological river types were defined using bioregions or large rivers, and nine natural environmental descriptors recognised in literature as being important for river community composition in Slovenia. The rivers’ ecological status is assessed based on two biological elements, phytobenthos and macrophytes, and on benthic invertebrates, whereas an assessment system for fish is still under development. Phytoplankton rarely occurs in Slovenian rivers; therefore phytoplankton-based assessment systems were not developed. The Slovenian river classification system consists of three modules with pressure-specific assessment methods. The impact of three groups of pressures is assessed: organic pollution (saprobity), nutrient load (eutrophication) and hydromorphological alterations/general degradation. Phytobenthos and macrophytes are used to assess river saprobic and trophic status, whereas benthic invertebrates are used to assess saprobity and impact of hydromorphological alteration/general degradation. In our study, the impact of hydromorphological alterations of the Drava River was assessed using benthic invertebrates. A Slovenian multimetric index SMEIH was calculated at fifteen sampling sites. Good to bad ecological status was assessed. Moreover, at most sites within the Heavily Modified Water Bodies of the Drava River, good ecological potential was not achieved. In conclusion, mitigation measures are needed on the Drava River in order to achieve objectives of the Water Framework Directive.

Application of indicators of hydrologic alterations in the designation of heavily modified water bodies in Spain

Abstract In Europe, the Water Framework Directive (2000/60/EC) demands the achievement of a good ecological status for water bodies by 2015. However, it also defines exceptions to these objectives, such as a good ecological potential instead of a good ecological status or a more distant temporal horizon than 2015. Those exceptions may only be applied to heavily modified water bodies (HMWBs). This paper presents a method, P-IAHRIS, incorporated into the free software IAHRIS v2.2, that offers objective criteria for the preliminary designation of HMWBs downstream from irrigation dams, flood protection dams or drinking water supply dams. The procedure incorporates two indicators: (i) the P10%–90% indicator, which analyses the alterations in the flow regime associated with the range of natural variability defined by the 10th and 90th percentiles of the annual and monthly discharges; and (ii) the IHA-HMWB indicator, which assesses the changes in the magnitude, seasonality, variability and duration of natural flows. P-IAHRIS was applied to 103 water bodies in Spain. The functionality and versatility of the method have been proven and allow the fast and objective preliminary designation of HMWBs, both in the Mediterranean and Atlantic environments.

Analysis and evaluation of large‐scale river restoration planning in Germany to better link river research and management

AbstractIn December 2008, the draft programmes of measures (PoM) have been published in the EU member states, which list the measures that will be taken to enhance the ecological status of surface and groundwater bodies, and to reach the environmental objectives of the EU‐Water Framework Directive (WFD). We have analysed the German PoM to identify the main pressures and the restoration measures water managers planned to implement in streams and rivers. The objective was to evaluate the PoM and to identify the main, practically relevant knowledge gaps in river management on which applied river research should focus on.In general, the selection of measures in the PoM was reasonable. In accordance with the analysis of pressures and impacts in Germany, the PoM focussed on measures addressing morphological alterations and river continuity, and the results indicated that diffuse source pollution and fine sediment input were additional main pressures in Central European streams and rivers. Although point source pollution was not a main pressure in most rivers, respective point source measures have been selected for many water bodies. Apparently, these were so‐called basic measures that have to be taken due to other EU‐Directives or national laws. Therefore, although in line with the WFD, it seemed doubtful if the point source measures would help to substantially enhance the ecological status. Furthermore, the results indicated that there was a general lack of knowledge on the effect of restoration measures and a specific knowledge gap in how to enhance the ecological state of heavily modified water bodies (HMWB) in the lowland region with a high land‐use pressure, which was reflected by the high share of water bodies for which conceptual measures have been selected (e.g. developing management plans).Based on the analysis of the PoM and a literature review, we identified the following, practically relevant knowledge gaps in river management: (i) the morphodynamics of river reaches where natural channel dynamics have been restored, (ii) the combined effect of measures addressing diffuse nutrient and fine sediment input at different spatial scales (e.g. riparian buffer strips and land‐use changes), (iii) methods to identify suitable and efficient measures and to define environmental objectives for HMWB and (iv) the effect of measures on less well‐studied biological groups like macrophytes and phytoplankton. There is a strong need to summarize recent research results on these issues, to identify the knowledge gaps and research needs in detail, and to make the results of such a comprehensive literature review or meta‐analysis available for the next 6‐year management cycle and second WFD management plans. Copyright © 2010 John Wiley & Sons, Ltd.

Towards ecological goals for the heavily modified lakes in the IJsselmeer area, The Netherlands

The European Water Framework Directive (WFD) obliges EU member states to define ecological goals for water bodies and, if necessary, to take measures to achieve these goals by 2015. The goals and measures for the water bodies in the IJsselmeer area of The Netherlands are elaborated in this study, following an approach described by Irmer & Pollard (2006, Alternative methodology for defining Good Ecological Potential (GEP) for Heavily Modified Water Bodies (HMWB) and Artificial Water Bodies (AWB). ECOSTAT). With the closure of the Afsluitdijk in 1932, the former Southern Sea estuary was transformed into the freshwater Lake IJsselmeer. Subsequently, a string of so-called border lakes and Lake Markermeer were created by land reclamation projects and the construction of dams. These alterations serve safety, provide drinking water supplies and created agricultural land. Owing to the change in category, the lakes are by (WFD) definition heavily modified. A natural lake rather than an estuary will be the starting point for determining ecological potential. However, damming and fixing the water table prevented the development of emergent vegetation and caused steep water-land gradients. The Maximum Ecological Potential includes the effect of these hydromorphological changes after all mitigation measures have been considered. Other pressures on the lakes are high nutrient loads, which cause phytoplankton blooms, the disappearance of aquatic macrophytes and intensive fishery, which overexploites the pikeperch and eel populations and causes indirect negative effects on water quality. Good Ecological Potential for these lakes is derived by estimating the effects of all effective hydromorphological measures that have no significant negative impact on existing functions or the wider environment, and the effects of all other measures. The suggested main measures are: construction of fish passages, adaptation of shore-lines, wind sheltered areas, reduction of nutrient load, reduction of fishery pressure and reduction of the bream stock. The effects of these measures are calculated from multivariate analyses that establish the relationships between (a) nutrients and chlorophyll-a, (b) chlorophyll-a and water transparency, (c) water transparency, depth distribution and vegetation coverage and (d) vegetation coverage and fish community. The proposed goals will be refined using new scientific insights and further discussions with stakeholders, and will finally be reported in the River Basin Management Plan 2009. It is expected that exemptions will be used for a phased achievement of the objectives.