Water quality in the Lake Illawarra catchment

Abstract

Lake Illawarra has a land catchment of 235 km2, through which several creeks and streams pass into the Lake. Data from three local council and one DIPNR water quality monitoring projects, within the Lake Illawarra catchment, have been compared and analysed in order to assess the current state of these waterways and their possible impact on Lake Illawarra. Data from the same or similar projects in Wollongong, Wingecarribee and the Georges River were used for comparison. Water quality in the two major catchments draining into Lake Illawarra - Macquarie Rivulet and Mullet Creek - differed significantly in terms of dissolved oxygen, turbidity, pH, nutrients and conductivity, reflecting the greater development in the Mullet Creek catchment. The anticipated further development of Mullet Creek is likely to exacerbate the poor water quality in this catchment, with most indicators already outside ANZECC guidelines (2000). Past and present coal mining activities appear to be contributing to elevated conductivity and pH in affected sub-catchments and other Wollongong streams. Changes to pH and conductivity may have direct or indirect ecosystem impacts. The causes of elevated wet and dry weather faecal coliform counts are currently unclear; this situation is unsatisfactory as faecal coliform counts in Wollongong streams are rarely below ANZECC primary contact guidelines (2000). Source control of sediment and nutrients is recommended for the protection of both Lake Illawarra and the waterways themselves. Community appreciation and ownership of these waterways is critical for the successful maintenance of good water quality.