Eutrophic Lake Water Research Articles

Inter- and intra-specific differences in filtering activities between two unionids, Anodonta woodiana and Unio douglasiae, in ambient eutrophic lake waters

Inter-specific and intra-specific differences in the filtering activities of two unionid bivalves, Unio douglasiae and Anodonta woodiana, which thrive in small agricultural canals, were compared using a flow-through chamber system of ambient eutrophic lake water. The mean filtration rates (FRs) of these two species, size-matched for similar shell length, were not significantly different ( t-test, t = 0.024, P = 0.981), whereas there were significant differences in the FRs between mussels of different ages ( t-test, t = 5.137, P = 0.001), different densities ( t-test, t = 8.297, P < 0.0001), and different currents ( t-test, t = 3.898, P = 0.005). The FRs of A. woodiana increased significantly more with higher temperatures in younger mussels ( P < 0.01, maximum FR = 0.352 ± 0.157 L/h at 13.5–20.4 °C) than in adults. However, the mortality of the mussels was comparatively higher in younger mussels due to a low tolerance to ammonia. Correlation coefficients and PCA results collectively indicate that the two dominant unionid mussels in the canal had a strong relationship with the seston level in the lake (turbidity, suspended solids and chlorophyll- a), resulting in a higher FR, pseudo-faeces production, and ammonia tolerance and a lower mortality. In addition, the validation of the biomanipulation used in the mussel-controlled system is discussed in an effort to improve the water quality of eutrophic lakes and streams and the conservation of the benthic mussel community.

Temporal and spatial variations of low-molecular-weight organic acids in Dianchi Lake, China

Low-molecular-weight organic acids (LMWOAs) in eutrophic lake water of Dianchi, Southwestern China Plateau were investigated diurnally and vertically using ion chromatography. Two profiles (PI and P2) were studied due to the difference of hydrochemical features. Lactic, formic, pyruvic and oxalic acid were detected as major components at PI and P2 which were on average 7.98 and 6.53 μmol/L, respectively, corresponding to their proportions of 2.68% and 2.48% relative to DOC. Pyruvic acid was regarded as the uppermost species at PI and P2, reaching up to 3.82 and 3.35 μmol/L and accounting for 47.9% and 51.3%, respectively, in individual TOA. Although humus were of biogenetic production at both sites, the significant negative correlation between diurnal variations of TOAs, fluorescence intensity (FI) of protein-like components and humic-like components at PI indicated LMWOAs were greatly originated from bacterioplankton excretion and degradation. However, correlations between diurnal variations of humic-like FI and physicochemical parameters demonstrated algal origination of LMWOAs at P2. Although content of humus was high, TOA at P2 was 1.45 μmol/L lower than that at PI, due to the co-influence of more intense photo-oxidation and aggregation at P2. Therefore, TOAs exhibited quite opposite diurnal variation trends of increasing-decreasing and decreasing-increasing at PI and P2, respectively. Except for impact of solar radiation, bacterial decomposition and assimilation rendered shifts of maximal LMWOAs along water column at PL Covering with massive algae, UV rays penetrated shallower depth that LMWOAs assembled in surface layer water before 18:00 at P2 and represented decreasing profiles.

Runoff effect on eutrophic lake water quality and heavy metal distribution in recent littoral sediment

Multivariate statistical methods (hierarchical clustering analysis: HCA, and principal component analysis: PCA) were used to study the influence of runoff and other diffuse pollution sources on lake water chemistry of Hough Park lake in Central Missouri. In addition, heavy metal concentrations in lake littoral sediment were evaluated for enrichment and probable ecological risk. The abundance of macronutrients in the lake water column followed the order: Ca > Mg > TIC > K > Na > S > NO 3 – N > Fe > NH 3 – N > TP. Heavy metal concentrations in the lake water column were below acute and chronic level ecological guidelines. TN:TP ratios (range: 4.1–6.8) revealed nitrogen limitation of algal and other photosynthetic plant growth. The HCA showed two major clusters of similarity between the sampling points suggesting different pollution levels for the clusters. PCA 1, 2 and 3 reflected the influence of natural biochemical processes, atmospheric deposition and runoff respectively on lake water chemistry. The abundance of heavy metals and the normalizing element (Li) in littoral sediment (<63 μm fraction) samples analyzed in decreasing order were: Mn > Zn > Cr > Ni > Li > Cu > Pb > Cd > Hg. The average concentration of Cr, Mn and Ni in littoral sediment fraction exceeded the respective lowest effects level (LEL) threshold limit. Metal bioavailability in sediment fraction was low since the most labile metal species contained between 0% and 11% of the total metal content. Using the risk assessment code (RAC) criteria, only Mn posed a medium risk to the lake system.

Bio-treatment of phosphate from synthetic wastewater using Pseudomonas sp YLW-7

In this study, the efficient phosphate utilizing isolates were used to remove phosphate from synthetic phosphate wastewater was tested using batch scale process. Hence the objective of the present study was to examine the efficiency of bacterial species individually for the removal of phosphate from synthetic phosphate wastewater. The most efficient phosphate reducers were isolated and screened from eutrophic lake water samples. The total heterotrophic bacterial analysis of the samples showed the presence of about 22 phosphate reducers. Among them, Pseudomonas sp YLW-7 were found to be efficient in phosphate reduction based on the maximum phosphate ultization which was observed by plate screening method using the minimum inhibitory concentration (MIC) test. The effect of carbon sources (glucose, starch, sucrose and lactose) at 0.5% on the removal of phosphate by Pseudomonas sp YLW7 was estimated. The maximum growth of Pseudomonas sp YLW7 was observed to be 0.9886 OD in glucose followed by starch (0.9456 OD), Sucrose (0.9095 OD) and lactose (0.8407 OD). The pH change in culture medium after 72 h treatment was found to be 6.0 in glucose, starch, lactose sources and 5.8 in sucrose carbon source. The phosphate removal was observed to be maximum of 68 % in synthetic phosphate wastewater with glucose carbon source followed by starch (66%), sucrose (65%) and lactose (62%) after 72 h at neutral pH (7.0± 2) by Pseudomonas sp YLW-7. Thus the Pseudomonas sp YLW-7 may use the contaminants as nutrients source and might be used in the remediation of phosphate contaminated environments.

Eutrophication of Lake Waters in China: Cost, Causes, and Control

Lake water eutrophication has become one of the most important factors impeding sustainable economic development in China. Knowledge of the current status of lake water eutrophication and determination of its mechanism are prerequisites to devising a sound solution to the problem. Based on reviewing the literature, this paper elaborates on the evolutional process and current state of shallow inland lake water eutrophication in China. The mechanism of lake water eutrophication is explored from nutrient sources. In light of the identified mechanism strategies are proposed to control and tackle lake water eutrophication. This review reveals that water eutrophication in most lakes was initiated in the 1980s when the national economy underwent rapid development. At present, the problem of water eutrophication is still serious, with frequent occurrence of damaging algal blooms, which have disrupted the normal supply of drinking water in shore cities. Each destructive bloom caused a direct economic loss valued at billions of yuan. Nonpoint pollution sources, namely, waste discharge from agricultural fields and nutrients released from floor deposits, are identified as the two major sources of nitrogen and phosphorus. Therefore, all control and rehabilitation measures of lake water eutrophication should target these nutrient sources. Biological measures are recommended to rehabilitate eutrophied lake waters and restore the lake ecosystem in order to bring the problem under control.

Study on bioremediation of eutrophic lake

Bioremediation is considered as one of the effective ways to deal with the pollution of natural water because of its high efficiency, low cost and causing no secondary pollution. The multiple microbial preparation is composed of bacteria that can transfer nutritive material harmless and some natural humic acid which can destroy algae. The qualified bacteria were selected, separated, and enriched from the water and bottom sediment of eutrophic lake. A field trial of bioremediation was carried out in 60 m 3 of eutrophic water body in Yingze Lake of Anshan for four months. TN (total nitrogen), TP (total phosphorus), ammonia nitrogen, COD Cr, and turbidity of the trial water and untreated water were measured termly. Contrastive analysis showed the mulriple microbial preparation can increase the water capacity of self-purification, decrease the turbidity, inhibit algae growth and improve water quality gradually at substantially lower cost. Thus the problem of lake eutrophication can be solved radically by bioremediation.

Enhanced nitrogen and phosphorus removal from eutrophic lake water by Ipomoea aquatica with low-energy ion implantation

Ipomoea aquatica with low-energy N + ion implantation was used for the removal of both nitrogen and phosphorus from the eutrophic Chaohu Lake, China. The biomass growth, nitrate reductase and peroxidase activities of the implanted I. aquatica were found to be higher than those of I. aquatica without ion implantation. Higher NO 3–N and PO 4–P removal efficiencies were obtained for the I. aquatica irradiation at 25 keV, 3.9 × 10 16 N + ions/cm 2 and 20 keV 5.2 × 10 16 N + ions/cm 2, respectively ( p < 0.05). Moreover, the nitrogen and phosphorus contents in the plant biomass with ion implantation were also greater than those of the controls. I. aquatica with ion implantation was directly responsible for 51–68% N removal and 54–71% P removal in the three experiments. The results further confirm that the ion implantation could enhance the growth potential of I. aquatica in real eutrophic water and increase its nutrient removal efficiency. Thus, the low-energy ion implantation for aquatic plants could be considered as an approach for in situ phytoremediation and bioremediation of eutrophic waters.

Mechanisms and assessment of water eutrophication

Water eutrophication has become a worldwide environmental problem in recent years, and understanding the mechanisms of water eutrophication will help for prevention and remediation of water eutrophication. In this paper, recent advances in current status and major mechanisms of water eutrophication, assessment and evaluation criteria, and the influencing factors were reviewed. Water eutrophication in lakes, reservoirs, estuaries and rivers is widespread all over the world and the severity is increasing, especially in the developing countries like China. The assessment of water eutrophication has been advanced from simple individual parameters like total phosphorus, total nitrogen, etc., to comprehensive indexes like total nutrient status index. The major influencing factors on water eutrophication include nutrient enrichment, hydrodynamics, environmental factors such as temperature, salinity, carbon dioxide, element balance, etc., and microbial and biodiversity. The occurrence of water eutrophication is actually a complex function of all the possible influencing factors. The mechanisms of algal blooming are not fully understood and need to be further investigated.

Variability of bio-optical parameters in two North-European large lakes

The bio-optical properties of some North-European large lakes were examined during 1995–2005 using field data and laboratory measurements. The key variables were optically active substances (OAS: chlorophyll, total suspended matter and dissolved organic matter), Secchi depth, and the “spectrometric” and diffuse light attenuation coefficients. Our main study sites were Lake Peipsi and Lake Vortsjarv in Estonia, both eutrophic with mean Secchi depth below 3 m. The measured water parameters were compared with those obtained from two clear-water Swedish lakes, Lake Vanern and Lake Vattern. This comparison describes the biooptical differences of the water in eutrophic and oligotrophic lakes. The variability of water parameters in the turbid Estonian lakes was rather high, e.g. the chlorophyll content varied from 1.8 to 102 mg m−3 and the diffuse light attenuation coefficient from 0.92 to 6.5 m−1. The change in water properties depends on the season and the biological activity of phytoplankton. We found no apparent long-time trend in water properties. Regression analysis showed that in the turbid Estonian lakes the optical properties were well correlated with chlorophyll and suspended matter, but not with dissolved organic matter. The highest determination coefficients (between 0.73 and 0.89) were obtained when the optical parameters were correlated with all three OAS together (multiple regressions). Our results concerning the variability and interconnections among bio-optical parameters in two Estonian large lakes illustrate the effect of OAS and light field on the ecological conditions of lakes in general.

Potential of constructed wetlands in treating the eutrophic water: Evidence from Taihu Lake of China

Three parallel units of pilot-scale constructed wetlands (CWs), i.e., vertical subsurface flow (VSF), horizontal subsurface flow (HSF) and free water surface flow (FWS) wetland were experimented to assess their capabilities in purifying eutrophic water of Taihu Lake, China. Lake water was continuously pumped into the CWs at a hydraulic loading rate of 0.64 m d −1 for each treatment. One year’s performance displayed that average removal rates of chemical oxygen demand (COD), ammonia nitrogen ( NH 4 + – N ) , nitrate nitrogen ( NO 3 - – N ) , total nitrogen (TN) and total phosphorous (TP) were 17–40%, 23–46%, 34–65%, 20–52% and 35–66%, respectively. The VSF and HSF showed statistically similar high potential for nutrients removal except NH 4 + – N , with the former being 14% higher than that of the latter. However, the FWS wetland showed the least effect compared to the VSF and HSF at the high hydraulic loading rate. Mean effluent TP concentrations in VSF (0.056 mg L −1) and HSF (0.052 mg L −1) nearly reached Grade III (⩽0.05 mg L −1 for lakes and reserviors) water quality standard of China. Wetland plants ( Typha angustifolia) grew well in the three CWs. We noted that plant uptake and storage were both important factors responsible for nitrogen and phosphorous removal in the three CWs. However, harvesting of the above ground biomass contributed 20% N and 57% P of the total N and P removed in FWS wetland, whereas it accounted for only 5% and 7% N, and 14% and 17% P of the total N and P removed in VSF and HSF CWs, respectively. Our findings suggest that the constructed wetlands could well treat the eutrophic lake waters in Taihu. If land limiting is considered, VSF and HSF are more appropriate than FWS under higher hydraulic loading rate.

Inverse Data Modelling for the Optical Properties of the Eutrophic Lake from Reflectance Spectra in Nanhu Lake of Changchun, China

In this study, we present an inverse data modelling for the optical properties of the eutrophic water from reflectance spectra in Nanhu Lake of Changchun, China. The lake water in Nanhu Lake is optically dominated by scattering from suspended matter, whereas the lake water is dominated by absorption from phytoplankton (CHLa), total suspended matter (TSM), and coloured dissolved organic matter (CDOM or referred to as yellow substance). The main reason is that the Nanhu Lake is highly affected by the input from rivers and drainage systems from the area of Changchun, which discharge a high concentration of CDOM, nutrients, and mineral suspended solids. The reflectance spectra at 400–900 nm were measured in Nanhu Lake using the ASD-field spectroradiometer. An inverse data modelling was applied to analyse the optical properties of the eutrophic lake water. The result shows that the optical properties of the eutrophical water can be effectively modelled from reflectance spectra for the eutrophic lake. However, further studies are still needed to refine the method for determining the optical properties of eutrophic waters under study.

Laboratory investigation of the phosphorus removal (SRP and TP) from eutrophic lake water treated with aluminium

Mechanisms involved in phosphorus (P) removal from eutrophic lake water with aluminium (Al) were assessed by jar tests. For this purpose, eutrophic lake water enriched with soluble reactive phosphorus (SRP), algae or sediments in order to mimic the various conditions found in shallow eutrophic lakes was studied. Total phosphorus (TP) removal was reached after floc settling, the maximal TP removal efficiency (90–95%) was obtained for an Al concentration ranging from 2 to 5 mg L −1, depending on the organic matter (OM) origin (algae or sediments). Algae appeared to limit macro-floc formation (those able to settle). In contrast, in the presence of sediments, macro-floc formation was favoured at low Al dose (2–3 mg L −1 Al). High SRP removal was obtained with the lowest Al dose (1 mg L −1 Al) and remained greater than 60% for an SRP concentration up to 350 μg L −1. SRP removal was not influenced by the OM origin. The experimental data and literature were used to suggest a hypothetical model for floc formation and P removal with Al under the conditions observed in treated lakes.

Monitoring Algal Toxins in Lake Water by Liquid Chromatography Tandem Mass Spectrometry

Microcystins (MCs) and cylindrospermopsin (CYL) are potent natural toxins produced by cyanobacteria (blue-green algae) that grow worldwide in eutrophic freshwaters and cause animal and human water-based toxicoses. The main purpose of this work has been assessing the contamination levels of some MCs and CYL in eutrophic Italian lake (Albano) water. To do this, we have developed an original analytical method involving MC extraction with a sorbent (Carbograph 4) cartridge. CYL is a highly polar compound that is scarcely retained by any sorbent material. To analyze this toxin, we directly injected 0.5 mL of filtered lake water into the liquid chromatography (LC) column. Analytes were quantified by LC coupled to tandem mass spectrometry in the multireaction monitoring mode. The recovery of five selected MCs added to an analyte free lake water sample at three different concentrations (50, 150, and 500 ng/L) ranged between 93 and 103% with RSD values no larger than 8%. Limits of quantification (LOQ) of the five MCs were within the 2-9 ng/L range, whereas the LOQ of CYL was 300 ng/L. The occurrence and abundance of cyanotoxins in Lake Albano was monitored over four months (Sept-Dec 2004) by analyzing water samples collected monthly at the center of the lake and at different depths (from 0 to -30 m). During survey and with the MS/MS system operating in the parent ion scan mode, we individuated two demethylated forms of MC-RR and one demethylated variety of MC-LR. Demethylated MC-RRs are known to be even more toxic than MC-RR toward zooplanktic grazers. CYL was the most-abundant toxin during the first three monitoring months. To the best of our knowledge, this is the first work reporting concentration levels of CYL in lake water.

Development of Temporal Temperature Gradient Electrophoresis for Characterising Methanogen Diversity

Temporal temperature gradient electrophoretic (TTGE) analysis of 16S rDNA sequences was optimized to monitor the methanogen population present in water and sediments of a small eutrophic lake, Priest Pot, in the English Lake district. The production of nonrepresentative TTGE profiles due to the generation of polymerase chain reaction (PCR) artifacts initially proved problematical. The use of a proofreading polymerase in the PCR was found to be essential and fully optimized protocols were established and tested to ensure confidence that the TTGE profiles truly reflected sequence diversity. TTGE analysis revealed the methanogen population to be less diverse in water than in sediment. The most genetic diversity was observed in TTGE profiles of sediment DNA isolated in winter and the least was in sediment DNA isolated in summer. DNA sequencing analysis of bands recovered from TTGE gels revealed the presence of two methanogen communities. One clustered with Methanosaeta species and the other with the Methanomicrobiales. Many sequences showed low DNA sequence similarity to known methanogens, suggesting that Priest Pot harbors previously undescribed methanogen species.

Pond or lake: does it make any difference?

Abstract: To investigate the importance of lake size, we analysed the chemical andbiological characteristics of nearly 800 Danish lakes ranging from 0.01 to 4200ha.Most of the lakes were shallow (median depth = 1.5m) and eutrophic (lake water meantotal phosphorus = 0.26mg P l –1 and mean chlorophyll-a = 60 µ gl –1 ). Phosphorus andnitrogen concentrations were unaffected by lake size, but positively related to agricul-tural exploitation. Lakes 1ha. The absence of fish did, however, not result in higher abun-dance of Daphnia , suggesting a higher impact by invertebrate predators in small lakes.Taxon richness of both zoo- and phytoplankton was weakly related to lake size,whereas the number of submerged macrophyte and fish species increased steadily withlake size. Also species richness of macrophytes increased with increasing alkalinity.The low impact of lake size on the species richness of several taxonomic groups sug-gests that ponds and small lakes are important biodiversity components in the agricul-tural landscape.Key words: catchment, phosphorus, phytoplankton, fish, zooplankton, macrophytes,biodiversity.

DEHP enrichment in the surface microlayer of a small eutrophic lake

Investigation of di-2-ethylhexyl phthalate (DEHP) in the surface microlayer (SM) and subsurface water (SSW) of a small eutrophic lake was carried out from April to June 2002. Results obtained from the field samples showed that tens to several hundred μg/L of DEHP was found in each sample of SM and SSW, indicating that the lake has been polluted by DEHP. Linear regression analysis showed that concentrations of DEHP were more strongly correlated with sampling temperature than with chlorophyll a concentrations. Correlation between DEHP concentrations and total phosphor concentrations was also obtained. Enrichment factors (EFs) of DEHP in the SM comparing with the corresponding SSW were ranging over 0.85–2.12 with an average of 1.35. DEHP EFs were significantly related to both enrichment of chlorophyll a in the SM and sampling temperature.

The discrimination of the response pattern of inter-phylum phytoplankton diversity to long-term eutrophication trends in Lake Kasumigaura, Japan

To study the response pattern of phytoplankton to eutrophication, the long-term water chemistry and biological data spanning three phytoplankton phyla and 19 genera were investigated in Lake Kasumigaura, a eutrophic lake in Japan. Fisher' s linear discrimination functions in combination with ecological indexes and a similarity index were used to analyze the relationship between the eutrophic levels (representing with dissolved inorganic nitrogen and total dissolved phosphorus) and the response of the inter-phylum phytoplankton diversity. The algal similarity index was found to characterize the change of eutrophication levels well. Almost 80 percent of eutrophic lake water samples can be correctly discriminated based on the logarithmic cells of phytoplankton genera. However, the ecological indices (number of genera, Margalef' s index, Menhinick' s index, McNaughton' s index, as well as the Shannon' s index and evenness index) failed to predict the change of eutrophic state.

A novel strategy for cyanobacterial bloom control by ultrasonic irradiation

The application of ultrasonic irradiation to control cyanobacterial blooms was evaluated in actual eutrophic lake water. Ten prototype units of the Ultrasonic Irradiation System (USIS) were installed in the 32 ha Lake Senba, and the water and sediment quality were monitored for 2 years. By incorporating the ultrasonication process with the on-going strategy, particularly flushing with induction water, cyanobacterial blooms can be controlled effectively. In addition, a significant improvement in the conditions of the lake in terms of chlorophyll-a, COD and T-P was attained. Moreover, the feasibility of ultrasonic irradiation and bacterial assisted control of cyanobacterial blooms was also evaluated in laboratory conditions. The destruction of gas vacuoles brought about by ultrasonic irradiation promoted close contact between cyanobacteria and their lysing Myxobacter leading to immediate and accelerated destruction of the cells.

Nutrient removal from eutrophic lake water by wetland filtration

Lake Apopka is a large (125 km 2), shallow (mean depth 1.6 m) lake in Florida, USA. The lake was made hypereutrophic by phosphorus loading from floodplain farms and has high levels of nutrients, phytoplankton (Chl a 80 μg l −1), and suspended matter. The restoration plan developed by the St. Johns River Water Management District encompasses the biomanipulation concept in which the critical step for large shallow lakes is increasing the transparency of the water to allow the re-establishment of submerged macrophytes. Restoration includes operation of a treatment wetland, reduction in external P loading, harvest of fish, fluctuation of lake levels, and littoral planting. The District constructed a 2-km 2 pilot-scale treatment wetland to test nutrient-removal and hydraulic performance. Lake water was recirculated for 29 months, and the removal of suspended solids and particle-bound nutrients was assessed. Hydraulic loading rate varied from 6.5 to 65 m year −l with a mean hydraulic residence time of about 7 days. The inflow contained 40–180 mg l −l TSS, 80–380 μg l −l TP (mostly particulate organic), and 3–9 mg l −l TN (mostly dissolved and particulate organic). Overall, particulate matter was removed (> 90%) by the wetland, and soluble organic compounds were unaffected. Soluble inorganic compounds such as nitrate, ammonia, and soluble reactive phosphate (SRP) were low in the lake water but increased during passage through the wetland. Particulate matter at the outlet was enriched in both N (2-fold) and P (5-fold) compared to particles in the inflow. Mass removal efficiencies were 89–99 (TSS), 30–67 (TP), and 30–52% (TN), but efficiency fell when hydraulic short-circuiting occurred. First-order removal coefficients were 107 (TSS), 63 m year −1 (TP) and 98 m year −l (particulate N). Areal particulate removal rates were 5.4 g dry matter m −2 day −l, 0.18 g PON m −2 day −l, and 0.006 g POP m −2 day −l. The ratio of N:P removal was 28:1. Total sedimentation rate was 0.4 mm day −l of very light matter (4.4 g dw l −l). About 40% of the dry matter and nitrogen removed and about 80% of the phosphorus was found in the new sediments. Relative to the inflow of lake water, evapotranspiration (4.3%), seepage (2.6%), and rainfall (2.8%) were low. Major problems were initial leaching of SRP, but not ammonia, from native organic soils and vegetation when this former farmland was flooded; hydraulic short-circuiting via former drainage ditches; and low inflows under drought conditions. After 6 months SRP release declined, and initial SRP leaching could be prevented with soil treatment. Hydraulic short-circuiting occurred only after modifications were made. Low gravity flows were augmented with pumped inflows. With these improvements P-removal should increase from the measured 0.48 to at least 3 g P m −2 year −l. Based on the pilot project results, the first phase of an improved 14-km 2 wetland filter has been constructed. This project should accelerate improvements in the water quality of Lake Apopka and, ultimately, create a new, large wildlife-rich marsh.

Observations on cyanobacterial population collapse in eutrophic lake water.

In two laboratory-scale enclosures of water from the shallow, eutrophic Lake Loosdrecht (the Netherlands), the predominating filamentous cyanobacteria grew vigorously for 2 weeks, but then their populations simultaneously collapsed, whereas coccoid cyanobacteria and algae persisted. The collapse coincided with a short peak in the counts of virus-like particles. Transmission electron microscopy showed the morphotype Myoviridae phages, with isometric heads of about 90 nm outer diameter and > 100-nm long tails, that occurred free, attached to and emerging from cyanobacterial cells. Also observed were other virus-like particles of various morphology. Similar mass mortality of the filamentous cyanobacteria occurred in later experiments, but not in Lake Loosdrecht. As applies to lakes in general, this lake exhibits high abundance of virus-like particles. The share and dynamics of infectious cyanophages remain to be established, and it is as yet unknown which factors primarily stabilize the host-cyanophage relationship. Observations on shallow, eutrophic lakes elsewhere indicate that the cyanophage control may also fail in natural water bodies exhibiting predominance of filamentous cyanobacteria. Rapid supply of nutrients appeared to be a common history of mass mortality of cyanobacteria and algae in laboratory and outdoor enclosures as well as in highly eutrophic lakes.