In recent years, low rainfall and over-allocation of water throughout the Murray-Darling Basin resulted in very low river flows reaching the Murray Mouth and Lower Lakes. Water levels in Lake Alexandrina and Lake Albert fell to lows that were unprecedented in thousands of years, disconnecting the two lakes.
Freshwater flows from the River Murray through the Murray Mouth are crucial to export salt and other pollutants from the entire Murray-Darling Basin, maintain water levels in the Lower Lakes and support a healthy Coorong ecosystem. Flows from the South East into the Coorong's South Lagoon are also important in maintaining the Coorong's health.
Investigations have been undertaken to determine the environmental water requirements of the region, ie how much water is needed to secure a healthy and resilient future for the region.
Work undertaken by Flinders University, Kerri Muller NRM and the Department of Environment, Water and Natural Resources has indicated that a range of flows, rather than a fixed volume of water, should be delivered to the region from year to year.
The proposed range of flows seeks to ensure:
- that the River Murray should flow out to sea every year, without the need for dredging to keep the Murray Mouth open
- that sufficient water should flow over the barrages to export salt and maintain salinity in the Lower Lakes below 1000 EC 95% of the time
- that water levels in the lakes should vary seasonally and between years
- that higher flows should be delivered as often as was historically the case, to keep the south lagoon of the Coorong in a healthy state.
Improved rainfall and inflows have raised water levels, the Lower Lakes have been reconnected, and water levels have equalised and have reached pre-drought levels.
Flows over the barrages and through the Murray Mouth are flushing salt from the lakes and providing much needed fresh water to the Coorong. The sea, Coorong and Lower Lakes are now reconnected for the first time since 2006.
The Murray-Darling Basin Authority has finalised a basin-wide plan that is changing the way water is allocated within and between states. It aims to provide more fresh water to protect and restore the region's environment.
Potential impacts of sea level rise
Sea level rise is not seen as an immediate threat to the Lower Lakes. The existing coastal dunes are expected to protect the lakes from increases in sea level.
Current predictions for South Australia are for sea level to rise at least 30 centimetres by 2050 and one metre by 2100. This may lead to a transition of the freshwater lakes to a more estuarine environment by the end of the century.