The recent tainted drinking water fiasco in Griffith highlighted the need to do something about Lake Wyangan. It blew the whistle on using Lake water for human consumption. Griffith Council and Murrumbidgee Irrigation (MI) should have applied the Precautionary Principle and Duty of Care.
They have persisted with using South Lake Wyangan water knowing that the health of that water was poor. They know that this Lake is a question mark for neurological disease and is a focus of universities for toxins variably produced by genera of cyanobacteria that may be involved with motor neurone disease. Whatever the case, using water from South Lake is risky. South Lake should be an ecological treatment wetland for its unmanaged catchment.
But wait, after years of nothing happening, North Lake is to be reclaimed for aquatic recreation. The essence of the only effective and low cost method is to improve light penetration and reintroduce submerged water plants to compete with cyanobacteria. This method is effective and practised elsewhere in the world.
The causeway between the two lakes is to be upgraded and as this happens a channel leading in to North Lake from the pump house will enable water to be drawn from North Lake. This will stop ‘amber’ and ‘red alert’ water being used.
Two parallel 10 m wide shallow wetlands (see sketch) will take a calculated flow of water from the supply system at the north end of North Lake 3 km to the causeway area. The slow flow, say 10-15 ML/day and a hydraulic retention time of c. 3 days, will enter the south east end of North Lake in the same channel that will enable MI to pump water to the Lake View Branch Canal. The wetlands could be a feature for the proposed subdivision on the eastern shore of North Lake. They will be used to reintroduce submerged plants into the Lake
Cumbungi, a major weed in Lake Wyangan, will be eradicated. Ideally it will be sprayed by helicopter, when water level has been dropped, to fully expose it. Complete kill can be achieved in April\May as it goes into winter senescence.
Catchment. The large agricultural catchment to the west only produces large runoff from heavy falls. This runoff needs to be contained and reused on farm.
South Lake can be turned into a shallow wetland system to rival Fivebough wetland at Leeton and draw the bird watching fraternity to its shores.
Geoff Sainty is an aquatic wetland specialist based in Griffith. He is the author of dozens of publications on freshwater plant species.