Lower Lakes Facts
Historically, the Lower Lakes and Coorong were never purely freshwater ecosystems. Seawater incursions occurred frequently during times of low river flows.
Abundant winter rains in 2010 and 2011 finally broke the Millennium Drought and replenished freshwater levels in Lake Alexandrina and Lake Albert. Whether through climate change or climate variability, it is inevitable that extended dry conditions will return again.
The facts remain:
Fact: Before 1940, the Lower Lakes were part of a vast estuary with the Coorong
Before the barrages were built in 1940, the Lower Lakes were part of the River Murray estuary, a vast estuarine ecosystem connected with the Coorong. The Lower Lakes and Coorong supported a range of ecosystems from freshwater to marine ecosystems. Learn why the mixing of fresh and salt water is so important. Read our collection of newspaper stories from the early 1900's at our blog.
Fact: A large percentage of the known Acid Sulphate Soil (ASS) sites would not be exposed if the Lower Lakes were maintained at sea level by opening the barrages
During a drought, the management "plan" is to keep the barrages shut and allow the Lower Lakes to dry down to -1.5m AHD, i.e., below sea level, then use bioremediation techniques to control the ASS. Of course, the latter would not form in the first place if the barrages were open and seawater allowed to mix with the freshwater.
Fact: The Lower Lakes as a freshwater ecosystem has been in decline for decades
The ecology of the Lower Lakes and the Coorong has been suffering biodiversity loss for decades, with loss of habitat, invasive fish species, such as carp, and declining native fish species. The presence of the barrages causes an abrupt change in the water environment and reduced tidal range, and is believed to be one of the major factors contributing to habitat degradation.
Fact: There is not enough freshwater during an extended drought to sustain the artificial freshwater regime of the Lower Lakes
During drought, there is not enough water in the Murray-Darling Basin storages to meet everyone's water needs. The CSIRO forecasts a long-term decline in flows at the Murray Mouth of up to 25% . It is estimated that the Lower Lakes require 4,000 to 6,000 GL per year (four to six thousands of billions of litres) of environmental flows to maintain a freshwater ecosystem. Read the FAQ for more information
Fact: The Lower Lakes evaporate up to 950 GL of freshwater each year
Disconnecting the Lower Lakes from the ocean has produced an annual requirement for 750 to 950 GL of freshwater to replace evaporative losses, which could instead be refilled by seawater. By comparison, greater Adelaide uses approximately 200 GL per year.