The Lower Lakes, Coorong and Murray Mouth icon site is an important ecological transitional area between the River Murray and the Southern Ocean as it passes through Lake Alexandrina, the Murray Estuary, the Coorong and, finally the Murray Mouth. These are the traditional lands and waters of the Ngarrindjeri people and their cultural significance is, in part, recognised through State Aboriginal Heritage listing. This diverse landscape accounts for much of its unique ecological qualities and the challenges in managing the area (DWLBC 2002). The complex ecology of the area has been changed by a system of barrages which isolate the Lower Lakes from the Murray Mouth and Coorong.
Surface water flow into the icon site is predominantly from the River Murray. Other surface water inputs include inflows via tributaries of the Eastern Mount Lofty Ranges into Lake Alexandrina and the Murray channel near Goolwa. Water of varying salinities, often brackish to saline also flows into the Coorong South Lagoon from the Upper South East Drainage Scheme via Salt Creek. Direct rainfall on the large surface area of Lakes Alexandrina and Albert is also an important source of freshwater input to the system. A series of barrages located between the islands in southern Lake Alexandrina separate the freshwater environments of the River Murray and Lower Lakes from the saline waters of the Murray Mouth estuary and Coorong (Figure : Map of the Lower Lakes, Coorong and Murray Mouth icon site. As a consequence, freshwater input to the Murray Mouth estuary and the Coorong during low flow periods are reliant on strategic barrage releases. Barrage and fishway releases help to establish a salinity gradient within the estuary and also facilitate ecological connectivity between the water bodies.
Lake Alexandrina (including islands) and Lake Albert
the lower reaches of the tributaries of the Eastern Mount Lofty Ranges
Murray Mouth estuary
Coorong (North and South Lagoons).
Physical conditions (e.g. salinity, occurrence and frequency of freshwater inputs) contribute to the complexity of the icon site and its ecological values. Parts of Lake Alexandrina and the Coorong (Kurrangk), and the Murray Mouth estuary, are registered as an Aboriginal site known as the Meeting of the Waters. The whole of the icon site is a Ngarrindjeri cultural landscape.
Lakes Alexandrina and Albert
Lakes Alexandrina and Albert are two large (c. 65,000 and c. 23,000 ha respectively) shallow lakes (depth typically <3 m) at the terminus of the Murray–Darling River system. The River Murray drains into Lake Alexandrina near Wellington. Lake Alexandrina is isolated from the Murray Mouth and Coorong by five barrages constructed between 1935 and 1940 which were constructed to provide freshwater for irrigation, stock and domestic use. Several islands lie within Lake Alexandrina, principally Hindmarsh and Mundoo which are adjacent to the Murray Mouth. Lake Albert is a terminal lake connected to Lake Alexandrina via a narrow channel known as the Narrung Narrows. Lake Alexandrina is the primary source of freshwater flow into Lake Albert.
Prior to European settlement, the Lower Lakes were predominantly fresh (Fluin et al. 2007; Fluin et al. 2011), with river water discharging to the sea keeping the Murray Mouth open. Saltwater intrusion to the Lower Lakes was not common until after 1900 when significant water resource development had occurred in the River Murray system (Sim & Muller 2004). Only small areas of the Lower Lakes, around the mouth and channels, would be impacted by saltwater intrusion during periods of low river flow or significant storm surges. Historically, the Lake Alexandrina / Murray Mouth interface would have been a spatially and temporally dynamic mosaic of wetlands with variable salinities.
The Eastern Mount Lofty Ranges tributaries of particular significance to the icon site include the Tookayerta and Currency creeks, and Finniss, Angas and Bremer rivers. The lower reaches of the Finniss River, and Tookayerta and Currency creeks lie within the boundary of the icon site. Although the Angas and Bremer rivers are outside the icon site boundary, their areas of confluence with Lake Alexandrina are ecologically important. The lower reaches of the Eastern Mount Lofty Ranges tributaries contain important wetland and aquatic habitats for bird, frog and fish communities. Generally, the tributaries are fed by unconfined aquifers and from annual rainfall that varies regionally from 350 mm to 850 mm. These freshwater inputs play an important role in maintaining the ecological complexity of wetland and aquatic habitats located within the lower reaches of these tributaries.
The Murray Mouth estuary includes the area from the Goolwa Barrage to Pelican Point. In average years, the area is naturally estuarine but salinity levels fluctuate depending on outflows and which barrage structures are used for releases. The estuary is ‘protected’ from the high-energy marine environment of the Southern Ocean by the Sir Richard and Younghusband peninsulas. The key factors determining the morphological condition of the Mouth and its adjacent estuarine channels are freshwater flow through the barrages and ambient coastal conditions and processes. Under (barrage) zero and low-flow conditions, water flow through the Murray Mouth is dominated by tidal flows. From October 2002 until December 2010, dredging was required to maintain an open Murray Mouth, maintaining tidal exchange between the ocean and the estuary.
The Coorong is a 140 km long, 2-3 km wide, shallow lagoon with a variable salinity regime. The salinity regime in the Coorong is typical of a ‘reverse estuary’ where salinity increases further from the estuary mouth. The Coorong comprises two lagoons which are divided by a headland (Parnka Point) which restricts the Coorong to a narrow (c. 100 m) channel. The North Lagoon of the Coorong extends from Pelican Point to Parnka Point and is characterised by similar conditions as the Murray Mouth estuary with barrage releases influencing salinity. The salinity gradient of the North Lagoon increases southwards towards Parnka Point. The hypersaline South Lagoon extends from Parnka Point to Salt Creek where it then becomes a series of hypersaline ephemeral lagoons. Freshwater inputs which historically entered through the southern end of the South Lagoon in winter/spring have decreased enormously since the end of World War II due to extensive drainage networks in the south east which now direct surface water runoff directly to sea.
The Lower Lakes, Kurrangk (Coorong) and Murray Mouth are central to Ngarrindjeri culture and spiritual beliefs. This association is expressed through creation stories (cultural and spiritual histories) about Yarluwar-Ruwe (Sea Country) which reveal the significance of the relationship between the country and the people, both practically and spiritually:
The land and waters is a living body. We the Ngarrindjeri people are a part of its existence. The land and waters must be healthy for the Ngarrindjeri people to be healthy.
Freshwater flows down the Murray–Darling system are seen by the Ngarrindjeri as the life blood of the living body of the River Murray, Lower Lakes and Coorong. Maintaining connectivity between parts of the living body is a Ngarrindjeri cultural priority.