Water for the Coorong, Lower Lakes, and Murray Mouth
In the Coorong, Lower Lakes and Murray Mouth (CLLMM), research shows that water levels in the Lower Lakes should be managed between 0.5 – 0.9 m AHD (Australian Height Datum), with a variable ‘flow regime’, rather than a fixed volume of water, ideally delivered to the region from year to year to enable a healthy wetland system.
A set of end-of-system flow requirements and ecological objectives have been determined for the CLLMM in the Long-term watering plan for the SA River Murray WRP Area (find it here, see page 48). Some of the specific ecological objectives include:
- maintaining or improving waterbird populations in the Coorong and Lower Lakes
- maintaining a spatio-temporally diverse fish community and resilient populations of key native fish in the Lower Lakes and Coorong
- maintaining or improving invertebrate communities in estuarine and lagoon sediments
- maintaining habitable sediment conditions in mudflats
- restoring aquatic vegetation in the Coorong and Lower Lakes.
Find out more about ecological objectives in the State of the Coorong - discussion paper from the Healthy Coorong, Healthy Basin program.
How water delivery works
Each year, water for the environment is delivered to the Lakes to help create a seasonally variable water regime, with peak levels in spring and summer and minimum levels in autumn. The variability benefits the ecology of the wetlands that fringe Lakes Alexandrina and Albert, as well as wetlands in the river channel weir pool between Lock 1 at Blanchetown and Wellington. Water for the environment also provides flow via the Lower Murray barrages and fishways.
If South Australia received no more than its annual entitlement flow (1,850 GL/pa), there would only be enough flow to keep water levels in the Lower Lakes at barely above minimum, without enough left to flow to the Coorong. This is why additional water – water for the environment – is critical in achieving end-of-system flows.
Water inflows to the CLLMM region come primarily from the River Murray into the north of Lake Alexandrina, near Wellington. Small, seasonal inflows also come from tributaries draining from the Eastern Mount Lofty Ranges to Lake Alexandrina, and from the Upper South East to the Coorong South Lagoon at Salt Creek. Marine water enters the Coorong estuary via the Murray Mouth.
Operating the barrages
Five barrages separate the freshwater of Lake Alexandrina from the more saline waters of the Coorong estuary. The barrages are Goolwa, Mundoo, Boundary Creek, Ewe Island and Tauwitchere. Each barrage contains at least one fishway, so fish can move freely, as does the flow control structure at Salt Creek.
| When | How the barrages operated |
|---|---|
| At different times of the year | Water for the environment is released at different locations across the 5 barrages. |
| At a minimum | All 11 fishways have continuous flow to support native fish movement and migration from the Coorong to upstream habitats. |
| For most of the year | Most of the available water is released from the Tauwitchere and Ewe Island barrages, which are the closest structures to the Coorong. This supports the productivity of the Coorong and a host of biota, including aquatic plants, invertebrates, fish, and waterbirds. |
| In winter | The proportion of flow is increased from the Goolwa barrage and, to a lesser extent, Mundoo barrage to direct flow to the Murray Mouth. The fresh water expels salinity and nutrients, keeps the Murray Mouth open, facilitates native fish (congolli and common galaxias) movement downstream from the Lower Lakes and facilitates upstream lamprey migration. |
Timing
Water for the environment is delivered to the Lower Lakes, Coorong and Murray Mouth Icon Site each year in-line with the SA River Murray Annual Environmental Watering Plan and Priorities (find it here). Extensive ecological monitoring helps in planning and prioritising when and where to deliver the water.
Water for the environment can be delivered to the CLLMM region all year round, particularly in very dry years to help maintain water levels in the Lower Lakes and continuous flow through the barrage fishways into the Coorong. Most water for the environment is delivered to the region in spring and summer, to best support the ecological needs of the Coorong during this time.
Does watering work?
Long-term scientific monitoring tracks the ecological condition of the region in connection with the goals listed above. Monitoring also informs decision-making around how we manage delivery of water for the environment.
The monitoring program includes vegetation, fish, waterbirds, benthic macroinvertebrates and water quality. Monitoring results are reported annually and are available here.
2020-21 marked the tenth consecutive year of continuous flows through the barrages, during which the River Murray has been continuously connected to the Coorong and Southern Ocean. Water for the environment has supported this connection, facilitating native fish movement and the export of salt from the Basin.
Highlights from 2023/2024 ecological monitoring
Plants
There was an improvement in submerged aquatic vegetation, and amphibious vegetation continued to be in good condition in the Lower Lakes in 2023-24.
However, the distribution and abundance of the aquatic plant Ruppia tuberosa was greatly reduced in the Coorong in summer 2023/24.
Fish
In February 2024, a black bream recruitment event occurred.
There was an exciting reintroduction of Yarra pygmy perch to the Lower Lakes.
High numbers of southern pygmy perch were recorded across the Lower Lakes.
Thousands of young-of-year congolli were detected moving upstream from the Coorong to Lake Alexandrina via barrage fishways.
11 pouched lamprey tracked moving upstream through barrage fishways.
Turtles
Evidence of Thukabi (turtle) recruitment also occurred at the Lower Lakes sites.
Macro invertebrates
Monitoring suggested bivalve and polychaete worms have expanded into the southern Coorong, likely due to freshening from the 2022-23 flood and continued unregulated flows and delivery of water for the environment in 2023-24.
Birds
In summer 2024, over 274,000 waterbirds were recorded in the Lower Lakes and Coorong.
50 different species were recorded in the Lower Lakes and 57 species in the Coorong.
Will access be affected?
Changing water levels in the Lower Lakes and Coorong do alter the area of land inundated, however access to and throughout the region is largely not affected by the delivery of water for the environment.
Water levels in the Coorong can alter significantly across seasons due to seasonal inflow fluctuations, evaporation rates, tides and swells, which may affect some accessibility to campgrounds in the South Lagoon. See the Coorong National Park website for park alerts on access.
How to stay informed
- Sign-up to receive the weekly River Murray Flow Report via email for information on when water levels will rise, expected water level depths and the expected duration. View previous reports.
- Visit the National Parks and Wildlife Service SA website
- Find out how to get involved in environmental water planning by contacting us at dew.ewater@sa.gov.au
- Subscribe to our mailing list to receive updates on your chosen location and hear about opportunities to get involved
