Yarrawonga weir is one of many structures that regulate the flow of the Murray. It raises the upstream water level to facilitate gravity-fed irrigation of farmland in Victoria and New South Wales. It also helps to mitigate flooding downstream and since 1994 has been used to produce hydroelectric energy with a 9.6 MW power station.
A unique feature of the weir is its fish lift system.
The lift operates on a daily cycle and works by attracting fish into a holding chamber using an auxiliary flow.
The floor of the chamber is then raised, allowing the fish inside to be identified and counted.
A silver perch (Bidyanus bidyanus):
A golden perch (Macquaria ambigua):
Once the data has been recorded a gate is opened to allow the fish to move upstream.
Whilst the pass appears to work for native species, including the Murray cod (Maccullochella peelii), there are doubts about the suitability of this system for passing juvenile and small-bodied fish.
And, as usual, not all fish find the entrance, leading to delays in migration, increased predation and disease risk, and potentially impacting reproductive fitness.
Downstream movement over the weir can also be problematic at low flow (<8,000 ml/day).
Martin // Adelaide