FAQs barrages, weirs and the Murray Mouth
Why is the Coorong, Lower Lakes and Murray Mouth important?
The Coorong, Lower Lakes and Murray Mouth Ramsar site has been recognised internationally as one of Australia’s most significant wetlands, satisfying at least eight of the nine criteria for listing under the Ramsar Convention.
The site is central to the life and culture of the Ngarrindjeri people, who continue to live on their traditional country. It is also the basis for a thriving community and a local economy with a focus on utilising the lakes for tourism or recreation and primary industries.
The site's 23 diverse wetlands are home to 119 species of waterbirds and 104 species of fish, along with a number of threatened species.
Salt and other nutrients from the entire Murray-Darling system are naturally washed out to sea through the Murray Mouth.
Why are the barrages in place?
As a result of upstream extraction, lower river flows allowed increasing volumes of seawater to intrude into the freshwater lakes, threatening the natural habitat of many of the systems’ unique species.
In 1931, the then River Murray Commission [CWLTH, NSW, VIC, SA] decided - after extensive investigation - and in lieu of reducing upstream extractions - to construct 5 barrages to help manage lake levels and improve water quality in the lower Murray and Lower Lakes system. Work on the Barrages commenced in 1935 and was completed in 1940.
Why aren’t the barrages opened and seawater allowed to enter the Lower Lakes?
South Australia and the Australian Government would be contravening the Environment Protection and Biodiversity Conservation Act 1999 (Cwlth) and the Ramsar Convention if the barrages were opened fully.
Under current arrangements there isn’t enough freshwater coming down from the upper Basin to stop seawater naturally entering the lakes.
A key priority is ensuring the freshwater environments of the site are protected from further seawater intrusions. While river levels remain low, the barrages continue to prevent seawater from destroying the region’s ecological character as a wetland of international importance.
Would there be water savings from opening the barrages?
Opening the barrages would require construction of a weir further upstream. A weir at Pomanda Island was investigated during the Millennium Drought as an option for maintaining water levels between Wellington and Lock. With a weir in place, a minimum through flow would be required to avoid major water quality issues upstream of the weir. It was found that the volume required would actually be sufficient to maintain suitable fresh water levels in the Lower Lakes, removing any necessity for a weir (or for the introduction of seawater).
How do we know the Lakes were predominately fresh?
There is significant evidence that the Lower Lakes were predominantly fresh water.
Ngarrindjeri traditional stories mention that the lakes were fresh. The plant and animal life that features in the stories are freshwater species. Ngarrindjeri were more or less permanently settled at the Lakes before European settlement, another indication that the lakes were freshwater.
Overlanders bringing stock from NSW in 1839 to the eastern shores of the Lakes report “waters quite sweet and fresh”.
Explorers such as Charles Sturt and various Surveyor Generals’ reported freshwater lakes.
Settlers drew water for domestic and stock from the lakes in the 1800s.
A productive Murray Cod fishery existed in the lakes in the 1800s.
An independent review of scientific studies about the Lower Lakes found they were largely freshwater prior to European settlement. This is informed by palaeoecological records, water balance estimates, hydrological and hydrodynamic modelling, traditional knowledge of the Ngarrindjeri People and anecdotal evidence of early explorers and colonists.
Recovery and protecting the CLLMM site
Since 2010, significant flows over the barrages, combined with increased flows from the South East, have brought salinity in the Coorong South Lagoon back within the targeted range and conditions have improved from the worst of the drought, however the ecosystem has been slow to respond, demonstrating the long-term nature of impacts associated with periods of low River Murray flows and extreme salinity.
The government is continuing to take action to restore the Coorong to full health through a suite of environment projects including our $70 million Project Coorong investment.
To find out more visit Project Coorong.