Central to the argument over the health of the Murray River and its environs is the demand from South Australia that the Lower Lakes, where the river meets the sea, must be maintained as freshwater lakes.
The Murray-Darling Basin Authority puts the position this way:
‘‘As more and more water has been diverted for human consumption, flow through the system to the sea has reduced by 75 per cent on average.
‘‘Water storage in dams and weirs changes the natural pattern (volume, timing and duration) of flow events through parts of the river system. It also prevents most of the natural small-to-medium sized floods that once occurred.
‘‘In the lower reaches of the system, many wetlands experience ‘man-made droughts’ in over 60 per cent of years (compared to natural droughts in five per cent of years, pre-development).
‘‘At the end of the system, the Coorong and lakes Alexandrina and Albert (the Lower Lakes), together a Ramsar site of importance for migratory shorebirds, have been particularly affected.
‘‘With reduced area of healthy wetland and floodplain woodland, and without flow triggers which stimulate waterbird breeding and fish spawning, many populations have been declining.
‘‘This is also occurring over many parts of the basin where the river has lost its connection with adjacent wetlands, creeks and flood-dependent forests.
‘‘Within a variable climate that includes decade-long drought (as recently experienced), the level of water use had become unsustainable.’’
This statement from an environmental water strategy concludes: ‘‘The aim of the Murray-Darling Basin Plan (and other water reform) was to address this but not to return freshwater ecosystems to a natural state rather, to deliver a healthy, working river system.’’
However some scientists and researchers have reached differing conclusions about what is a natural state for the Lower Lakes and how often seawater flowed into them.
Riverina farmer Louise Burge has spent years researching the history behind the Lower Lakes and made a number of points in a 120-page submission to the Murray-Darling Basin Authority:
‘‘The Murray River originally moved through a series of wetlands and swamps in its lower reaches before entering the estuarine waters of the Lower Lakes.
‘‘In high flow or flood events, there would be significantly increased fresh water flows into the Lower Lakes.
‘‘During periods of droughts or low flows, it was not uncommon for seawater intrusions to occur 250km upstream in the Murray River.
‘‘Salinity readings observed in 1914 show 1436 EC (electro conductivity units) at Morgan and 12373 EC at Murray Bridge. Salinity levels at the time, were attributed to marine influences.’’
Professor Peter Gell from the University of Ballarat challenges the notion that the lakes were always fresh.
He has examined core samples from lakebed sediment which led him to the conclusion that the lakes were partly salt for at least 6000 years.
His findings have raised discussions about what would happen if the barrages were removed and seawater was allowed into the lakes.
‘‘There is a precedent for sea-water naturally entering Lake Alexandrina,’’ Prof Gell has said.
He has raised questions over whether scarce freshwater resources should be allocated to a system that has been partly estuarine.
Victorian Shadow Water Minister and State Member for Euroa Steph Ryan points out the annual evaporation from the large lakes (about 700Gl) is almost equivalent to the water delivered in the Goulburn Murray Irrigation District in one year.
‘‘There needs to be more discussion about how South Australia uses engineering works to use water far more efficiently, rather than just looking towards the upstream states to keep sending more water down,’’ Ms Ryan said.
She raises questions over whether the perceived need to build a freshwater system in the lakes is driving the debate or whether it is about improving environmental outcomes.
‘‘We are sending huge volumes of water downstream to South Australia to maintain a freshwater ecosystem in these lakes.’’
■NEXT WEEK: Keeping the Murray mouth open.