Environmental water release underway to support Murray cod spawning in Lachlan catchment
A targeted environmental flow is under way in the Lachlan catchment to boost the breeding success of the iconic native fish, the Murray cod.
The action aims to trigger spawning movements, improve food availability and maintain stable water levels over nesting sites – critical steps in supporting the recovery of Murray cod.
The release is being managed by the NSW Department of Climate Change, Energy, the Environment and Water (NSW DCCEEW).
NSW licensed environmental water was released from Lake Brewster in mid-August. The first major pulse arrived at Booligal Weir on 31 August, ramping up to a peak of 700 megalitres (ML) per day for around 20 days. The flow stimulates fish movement, resuspends nutrients and creates a more productive aquatic environment after sustained low winter base flows of less than 100 ML a day.
‘This flow action is all about giving Murray cod the best chance to thrive,’ Senior Environmental Water Management Officer, Paul Doyle, said. ‘We’re aiming to provide ideal conditions for spawning, while also improving food availability and habitat quality. Without this environmental flow, the lower Lachlan River will continuously fluctuate up and down in line with irrigation cycles throughout spring.’
The action includes 2 key phases:
- Phase 1: Booligal Weir Pulse (late August–September)
A late winter–early spring flow pulse began on 31 August, with peak flows between 9 and 28 September. This aims to build pre-spawning body condition in Murray cod by enhancing food availability and habitat quality. - Phase 2: Hillston Weir Stable Flows (September–November)
From 19 September to late November, a stable flow of 400 to 500 ML/day will be maintained to support nesting and reduce the risk of eggs and larvae drying out. This ‘hydrological floor’ is essential to ensure consistent water levels over spawning sites.
‘Maintaining stable flows during the spawning season is key strategy,’ Mr Doyle added. ‘Sudden drops in water levels can expose nests and lead to egg loss. By holding a minimum flow, we’re helping protect the next generation of Murray cod.’
The initiative follows the ‘Fish and Flows’ conceptual model, which supports native fish recovery through seasonal flow management.
‘It’s a great example of how environmental water can be used strategically to support native species,’ Mr Doyle said.
‘We’re hopeful this action will lead to strong spawning outcomes and healthier fish populations in the Lachlan.’
Researchers from the Centre for Applied Water Science (CAWS) at the University of Canberra, supported by the Commonwealth Environmental Water Holder and researchers from NSW DCCEEW, will be out on the Lachlan River this spring, searching for larval Murray cod.
These early surveys will provide crucial insights into the success of recent environmental flows aimed at supporting cod spawning and recruitment.
‘If we find good numbers of larval cod in the system this spring – and the flows continue to support them – we could see a real boost in the population over the coming years,’ said Ben Broadhurst, fish biologist at CAWS. ‘It’s something we haven’t seen for a while, especially after disruptions caused by flooding over the past few years.’
‘It’s great that the team from NSW DCCEEW were able to add to this with an additional survey for larval Murray cod – it really adds robustness to the results and helps build a clearer picture of how the population has responded to the flows. A great opportunity to collaborate and co-learn across institutions!’ Broadhurst added.
The team from CAWS will return in autumn to survey juvenile cod between Forbes and Hillston, tracking how many of these larvae survived to grow into the next generation.
‘By delivering these flows, we’re giving Lachlan River Murray cod the best chance to do what they do naturally – spawn, recruit and thrive,’ Mr Broadhurst said.
