The Lower Lakes, Coorong and Murray Mouth icon site is located at the terminus of the River Murray system in South Australia. The icon site is bounded by the Mount Lofty Ranges to the west, the Murraylands to the north, the Upper South-east to the East and the Southern Ocean to the South. The principal towns are Goolwa at the western end of the icon site, Meningie on the shore of Lake Albert and Milang on the shore of Lake Alexandrina.
Boundaries of the Lower Lakes, Coorong and Murray Mouth icon site follow those of the Ramsar-listed Coorong and Lakes Alexandrina and Albert Wetland of International Significance. The icon site covers land and water areas totalling approximately 140,500 hectares incorporating the lagoons of the Coorong, Lakes Alexandrina and Albert, and the lower reaches of the Finniss River and Currency Creek (Figure : Map of the Lower Lakes, Coorong and Murray Mouth icon site), and includes:
all unallotted Crown Land and Crown Land occupied under licence that is connected to the lakes
wetlands on freehold and perpetual lease land, where the wetland is seasonally connected to the lake
all land and wetlands on Hindmarsh, Mundoo, Mud, Reedy, Ewe and Long islands and the many other small islands in the lakes
Tolderol, Mud Islands and Currency Creek Game Reserves
Salt Lagoon Islands Conservation Park
all land and water within the Coorong National Park.
The Lower Lakes, Coorong and Murray Mouth icon site consists of a range of different land tenures (Figure : Map of the Lower Lakes, Coorong and Murray Mouth icon site boundary and land tenure details. These include Conservation Park (i.e. Salt Lagoon Islands; 76 ha), Game Reserves (i.e. Currency Creek, Mud Islands and Tolderol; 428 ha), a heritage agreement (4 ha), the Coorong National Park (48,975 ha), other government land (including crown land) (4,034 ha) and private land (9,066 ha). The area is part of the traditional lands and waters of the Ngarrindjeri nation, the Ngarrindjeri & Ors (SAD 6027/98) native title claim and includes registered Aboriginal sites such as the ‘Meeting of the Waters’.
Figure : Map of the Lower Lakes, Coorong and Murray Mouth icon site boundary and land tenure details
2.3 Description of key ecological assets of the icon site
The Lower Lakes, Coorong and Murray Mouth icon site is comprised of four key environmental sub-regions, namely:
Lakes Alexandrina and Albert (Lower Lakes)
Eastern Mount Lofty Ranges tributaries
Murray Mouth estuary
the Coorong (North and South Lagoons).
Lakes Alexandrina and Albert (Lower Lakes)
The Lower Lakes are broad and shallow systems with unique and extensive fringing emergent vegetation. Much of the fringing vegetation is dominated by Phragmites australis with the most complex wetland flora found near the confluences of inflowing water bodies (e.g. creeks, drains) and islands. Fringing emergent vegetation has been simplified since the installation and operation of the barrages. Emergent macrophyte communities have thrived whilst communities dependent on variable water regimes have become restricted in their distribution (Phillips & Muller 2006).
Freshwater submerged aquatic plant communities were once extensive in the lakes system (Sim & Muller 2004) but are now restricted to near-shore habitats with good light penetration and low turbidity. Aquatic plant communities included species such as ribbon weed (Vallisneria australis), water ribbons (Triglochin procerum), pondweeds (Potamogeton spp.) and milfoils (Myriophyllum spp.). Submerged aquatic plants are now dominated by Potamogeton spp., Ruppia spp. and various types of charophytes; however, there has been an increase in abundance of Myriophyllum salsugineum, Vallisneria australis and Triglochin procerum since water levels were reinstated (Gehrig et al. 2011).
Many fringing wetlands around the Lower Lakes also support lignum (Muehlenbeckia florulenta) and samphire (e.g. Sarcocornia spp.) above the high water level. There are also remnant areas of swamp paperbark (Melaleuca halmaturorum)patchily distributed around Lakes Alexandrina and Albert (Marsland & Nicol 2009).
The EPBC-listed southern bell frog (Litoria raniformis)inhabits fringing wetlands of Lake Alexandrina, with known populations in Pelican Lagoon, Clayton Bay and Hindmarsh Island channels (Mason 2010; Mason & Hillyard 2011).
Hindmarsh, Mundoo, Ewe and Tauwitchere islands lie within a transitional zone between Lake Alexandrina and the Coorong. These island areas comprise unique vegetation communities. The freshwater habitats on, and immediately surrounding the islands are critical habitats for fish, particularly EPBC-listed small-bodied native fish such as Murray hardyhead (Craterocephalus fluviatilis) and Yarra pygmy perch (Nannoperca obscura). These transitional zones provide important ecological connectivity for migration of diadromous fish species such as congolli (Pseudaphritis urvillii)and common galaxias (Galaxias maculatus).
The area around Hindmarsh, Mundoo, Ewe and Tauwitchere islands are also where mudflats would have occurred before river regulation stabilised water levels. Mudflats in this area are now exposed over short time scales by wind seiching events and act as habitat for wading birds.
The lower reaches of the Finniss River, and Tookayerta and Currency Creeks are structurally diverse and support dense and diverse wetland habitats ranging from woodlands (e.g. river red gum (Eucalyptus camaldulensis)) to peat bogs. These areas also form part of the EPBC-listed ‘Swamps of the Fleurieu Peninsula’ ecological community and provide habitat for endangered species such as the Mount Lofty Ranges southern emu-wren (Stipiturus malachurus intermedius) (Phillips & Muller 2006).
In drought years, these tributaries act as critical refugia for many fishes and other species dependent on freshwater including the State-listed river blackfish (Gadopsis marmoratus)and the nationally-listed Yarra pygmy perch and southern bell frog (DEH 2010a; Mason 2010).
The lagoon environment of the estuary (from the Goolwa Barrage to Pelican Point) includes habitats such as exposed mudflats and shallow waters, which provide important foraging grounds for many wader bird species. In the past the vegetation community was dominated by Ruppia megacarpa, though this has not been present since 1986 (Hera-Singh, pers. comm. 2011), nor has it been recorded in the entire Coorong for a number of years (Nicol 2005).
An open Murray Mouth is critical for maintaining water quality in the estuary (through tidal exchange) and Coorong under zero and low flow conditions (Hemming et al. 2002). Tidal variations also facilitate daily inundation and exposure of mudflats, thereby maintaining invertebrate productivity and biomass in these areas (Dittmann et al. 2010). The Murray Mouth is considered open when the Diurnal Tidal Ratio (DTR) at Goolwa exceeds 0.3, with minimum DTR values of 0.05 and 0.2 at Tauwitchere and Goolwa respectively (DWLBC 2008). During high flows (around 35,000 ML/day) the DTR values at Goolwa and Tauwitchere are around 0.7-0.9 and 0.3-0.4 respectively.
The Murray Mouth estuary is an important transitional area for many species of fish that rely on estuarine conditions to complete their lifecycles.
The Coorong is highly regarded for its diversity and abundance of waterbirds (Wainwright & Christie 2008; Paton et al. 2009). Historically, the North Lagoon was mainly estuarine and provided rich, sheltered waters for fish and provided the necessary lifecycle cues required for aquatic seed germination, fish passage, breeding and foraging. Ruppia megacarpa was the dominant plant. Evidence suggests the South Lagoon was historically fresher than its current hypersaline state (Krull et al. 2009) and was freshened by winter/spring flows predominately from the South-east of South Australia. Increased salinity and unfavourable water levels in the South Lagoon over recent years, brought about by low freshwater inflows, have led to the severe decline of keystone species such as Ruppia tuberosa, chironomids and small-mouthed hardyheads (Atherinosoma microstoma).