Are the Lower Lakes of the River Murray historically freshwater lakes?

Depends on your definition of 'fresh'.  Since 1940, the barrages have maintained an artificial separation between freshwater and seawater.  This map from 1844 shows that around the Lakes the salinity levels varied. There are numerous historical reports of the Lakes being fresh in winter and spring and more salty in summer and autumn. There are historical reports that the lakes would also be saltier when there was drought in the Murray Darling Basin when Lake levels dropped and the seawater took it's place. 

Complaints from pastoralists, new farmers and dairymen about the Lakes becoming too salty to use became more frequent.  Fishermen in Goolwa and Milang found that the salty water brought mulloway. SA farmers blamed upstream irrigation diversions as the reason for low Lake levels. To this day, that assumption persists.

What would water levels be if the barrages were opened?

Seawater levels would vary with the tides (ref BoM Victor Harbor datum).  Tidal variation for the Lower Lakes would be lower due to the Murray Mouth and channels restricting water flows.

How much water do the Lakes lose to evaporation?

The Lakes lose 750 to 950 GL annually (ref MDBC) which is approximately 4 times Adelaide's annual water consumption.  See fast facts for more water stats.

GL = Gigalitre = 1,000 Megalitres or 1,000,000 Kilolitres or 1 billion litres

What are the water levels of the Lower Lakes?

See water level charts for average water levels for Lake Alexandrina, Lake Albert and the Goolwa Channel.

What are the problems confronting the Lower Lakes and Coorong?

The main problems are acidification, biodiversity loss, soil salinisation and desertification.  Read more..

What is the proposed Wellington or Pomanda Weir?

The proposed Wellington Weir is a temporary weir near Pomanda Island that will separate the River Murray from Lake Alexandrina. Read the Draft Environmental Impact Statement. The Supplemental Environmental Impact Statement (EIS) . (5MB)  Or the Executive Summary 

What is acid sulphate soil?

Acid sulphate soil (ASS) is the common name given to soils and sediments containing iron sulphides, the most common being pyrite. When exposed to air after being disturbed, soils containing iron sulphides produce sulphuric acid and release toxic quantities of iron, aluminium and heavy metals. Read more on acid sulphate soils.

What is the acidification water level trigger?

This is the level at which acidity being formed in the lake sediments can no longer be neutralized by the alkalinity of the sediments and lake waters. Any water levels below these will expose large areas of acid sulphate soils and any subsequent refilling (including future freshwater inflows or the introduction of

seawater) will likely result in the acidification of the water body. The current modelled critical acidification threshold water levels are minus 1.5m AHD for Lake Alexandrina and minus 1.0m AHD for Lake Albert.

What is paleolimnology?

Palaeolimnology is the study of past conditions in lake systems and the use of lake sediments to tell us about past environments. These techniques provide scientific evidence for the presence of seawater in Lake Alexandrina and Lake Albert.

What is an estuarine ecosystem?

Estuaries are coastal regions affected by both marine influences, such as tidal flows, and riverine influences, such as freshwater flows and sediments. Estuarine ecosystems typically support many biological niches resulting in high biological diversity.

How is salinity measured?

Salinity is measured according to the electrical conductivity (EC) of the water, in micro Siemens per cm at 25°C (μS/cm). 1 EC unit corresponds to  ~0.7mg/L of total dissolved salts; 1000 EC = 1000 μS/cm = 640 ppm. The salinity of seawater is approximately 50,000 EC. 

How much freshwater is available?

Not enough during an extended drought. For example, on 3 March 2010, the total active (useable) water in storage in the Murray Darling basin was 1,920 GL (Giga Litres), or 21% of capacity (ref MBDA). By comparison, approximately 1,200 GL was required to return the Lower Lakes to full supply level and a further 1000 GL of conveyance water would have been required to transport the water down the river.

Check the MDBA's Water in Storages website for up to date reports 

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