The History of the Fake Lower Lakes

The sea begins retreating from the Victorian border, forming a series of parallel “old Coorongs” at varying elevations, tilting northward toward the modern Coorong and Lower Lakes. These ancient lagoons facilitated natural freshwater flows from wetlands covering up to 50% of the South East region, recharged annually in winter.

Sea levels stabilise after a rise, expanding the Lower Lakes and depositing organic-rich clays that influence groundwater salinity. The Coorong forms as a dynamic estuary with significant groundwater discharge from the unconfined aquifer along its eastern shoreline, creating mixing zones with marine water.

Pre-European settlement. The South East is a mosaic of freshwater and saline wetlands (44–50% coverage), with large volumes of fresh groundwater and surface flows from the unconfined aquifer entering the Coorong at multiple points, including Salt Creek, Blackford Drain area, and near Bumyerie Island.

Lake Alexandrina is estuarine and often salty, while Lake Albert remains fresh due to aquifer inflows. Ocean water extends up to Pompoota (~270 km upstream), and the Murray Mouth stays open naturally. Aboriginal accounts describe abundant fresh springs (“Tengi”) and permanent dwellings with easy access to shallow fresh water.

Government survey of the Lower Lakes region records permanent Aboriginal dwellings near Lake Albert, with fresh water available at “trifling depth” and no need for wells, reflecting reliable aquifer discharge at the time.

Surveyor-General George Goyder recommends extending Maria Creek (which naturally drained only ~3 miles around Kingston SE) to alleviate local flooding around Millicent. A fateful recommendation that would reshape the hydrology of the entire South East.

First drainage works commence in the lower South East near Millicent and Port MacDonnell to manage waterlogging for agriculture and improve transport. Fresh water overflows the natural impediment at Tilley Swamp for five months, highlighting elevated wetlands slowly discharging into the Coorong via groundwater.

Narrow Neck Drain is dug as the first major public drain. The natural dam wall at Tilley Swamp is removed, accelerating drainage of elevated wetlands and redirecting flows away from the Coorong’s Southern Lagoon. This initiates compromise of the unconfined aquifer — a process that would accelerate dramatically over the following century.

South Eastern Drainage Act is passed, enabling Drainage Boards to levy landholders for maintenance and formalising expansion of the drainage scheme to reclaim waterlogged land for agriculture.

Maria Creek is extended into a major drain, capturing southern surface flows and redirecting water to the sea, further altering natural hydrology. What was once a 3-mile local creek becomes a regional drainage artery, cutting off the Coorong from its southern freshwater sources.

Lake Alexandrina is described as “salty and useless” for nine months of the year, with ocean water sometimes reaching Wellington. This predates upstream dams and locks, directly attributing early salinisation to South East drainage compromising the aquifer — not to upstream diversions.

Interstate Royal Commission on the Murray River investigates increasing salinity in the Lower Lakes. Using riverboat draft records dating back to the 1850s, it concludes boats could only operate six to seven months per year due to naturally low water levels. The Commission finds no systematic rise in salinity linked to upstream extraction.

Salinity impacts Lake Albert: reeds, willow, and gum trees die; first wells are sunk (some too salty to use). This marks Lake Albert as an early casualty of draining elevated wetlands, which had reversed its natural flow into estuarine Lake Alexandrina.

South East Drainage Act establishes the South Eastern Drainage Board to manage expanding drains, institutionalising and accelerating the destruction of the unconfined aquifer system that had sustained the Coorong for millennia.

The last full-blooded Ngarrindjeri Aboriginal, Milerum, laments in an Adelaide Chronicle article about the disappearance of fresh springs near the Coorong and landscape changes caused by drainage. An Indigenous perspective documents what scientific records would later confirm: a fundamentally altered water system.

South Australian Fisheries Commission report warns that proposed barrages will eliminate estuarine fish. The Commission doubts they will be replaced by freshwater species such as Murray cod, notes increasing Coorong salinisation from South East drains diverting fresh water away, and raises concerns that barrage construction would lead to shoaling (sandbank formation), posing navigation risks.

Construction of 7.6 km of barrages across Lake Alexandrina’s outlets transforms the Lower Lakes from a natural tidal estuary into an artificial elevated freshwater system. Lake levels are raised by up to 1 metre, increasing volume from 1,300 GL to 1,900 GL.

This restricts natural tidal mixing, reduces connectivity to the Coorong, and shifts reliance entirely to Murray flows for flushing — while drainage continues to diminish southern aquifer inputs. Bourman et al. (2000) note barrage construction reduced the tidal prism by 90%.

Barrages are closed for an entire year, yet the Murray Mouth does not close. This is a significant early data point — the system was still resilient enough to maintain itself without continuous Murray inflows, a resilience that would steadily erode over subsequent decades.

Surface flows from above Kingston and Salt Creek into the Coorong cease entirely due to drainage. Over 40,000 hectares are opened for agriculture, but wetland coverage collapses from around 50% to less than 6% — a loss of 44 percentage points of the region’s water-holding capacity in less than a century.

The Coorong begins showing visible ecological decline. Decaying organic material accumulates (now estimated at 6.4 mm per year in the Southern Lagoon), smothering the ecosystem as southern freshwater inputs fail. What was once a dynamic and productive estuary begins its long deterioration.

Professor Chris Von der Borch documents 18 inches of ephemeral freshwater flow extending from the Coorong’s Southern Lagoon to Kingston SE, highlighting multiple winter entry points beyond Salt Creek. This confirms the historical reality of distributed southern freshwater inputs — inputs that drainage had largely eliminated.

Severe drought; barrages are closed for 528 days, yet the Murray Mouth remains open. This outcome — the mouth staying open despite prolonged barrage closure — would become impossible just 13 years later, highlighting how rapidly the system’s resilience was deteriorating.

Floods force barrage openings; ocean water intrudes into Lake Alexandrina. This demonstrates the system’s persistent estuarine character and its natural tendency toward saltwater connection — suppressed only by the artificial management regime imposed since the 1930s.

The Murray Mouth closes after only 180 days of barrage closure — compared to the 528-day closure in 1967–68 when it stayed open. The system has lost the resilience it had just 13 years earlier, likely due to continued aquifer depletion and reduced southern freshwater inputs.

The Coorong, Lower Lakes, and Murray Mouth are listed under the Ramsar Convention as a “reverse estuary” dependent on Murray–Darling Basin flows. This listing overlooks the historical role of southern aquifer inputs and embeds an increasingly unsustainable management framework in international obligations.

The Upper South East Dryland Salinity and Flood Management Scheme is constructed — approximately 714 km of drains at a cost of around $200 million. Water is redirected to Blackford Drain and away from the Coorong’s Southern Lagoon. Completed in 2011, the scheme exacerbates hypersalinity in the Southern Lagoon.

The Millennium Drought. Prolonged dry conditions see barrages closed for 1,437 days with no flow to sea. Lower Lakes fall to 1 metre below sea level. A decision is made not to allow seawater in, exposing acid sulfate soils and concentrating salinity.

The Coorong experiences extreme eutrophication, hypersalinity, habitat loss, and failed species recruitment. The Murray Mouth requires continuous dredging from 2002 onwards. Vast volumes of freshwater are sent downstream from upstream communities to prop up an artificially elevated freshwater system.

Floods again show ocean intrusion into Lake Alexandrina when barrages are opened. Once again, the system demonstrates its natural estuarine character the moment artificial barriers are removed — confirming what the historical record has always shown.

The South East Coorong Restoration Flows Project is initiated, with approximately $60 million invested in attempts to address declining ecological conditions. Despite significant expenditure, the fundamental issue — the loss of southern aquifer inputs due to centuries of drainage — remains unaddressed by policy.