Fish count gets historic reservoir lowering on the hook

A fish population study at Warren Reservoir has revealed an estimated 16,000 fish, weighing a collective eight tonnes, call the reservoir home, with the data informing the storage’s gradual drawdown to enable SA Water’s upgrade of the dam’s 108-year-old intake and scour valves.

More than 2,600 healthy fish were caught during the study, underpinning the reservoir’s population estimate and found the most abundant native fish recorded to be Golden Perch – which, on average, measured 1.4 times greater in size than that found in the River Murray.

Modelling the drawdown provided insight into safely balancing the reduction in water levels while preserving dissolved oxygen levels, helping improve the survival rate of native fish during transfer to South Para Reservoir.

SA Water’s General Manager of Sustainable Infrastructure Amanda Lewry said based on the study’s learnings, the reservoir will be carefully lowered during a five-week period starting in March.

“This will be the first time we temporarily lower Warren Reservoir to near zero capacity, and we’ve invested the time to understand how we can preserve our valuable native fish while enabling an important capital project,” Amanda said.

“Over the past month, the South Australian Research and Development Institute, along with RecFish SA and its members, have been supporting our study by catching and tagging as many native fish as possible.

“The data they’ve captured has enabled our people to model the optimal reservoir drawdown, informing our timeline for lowering the water level and pinpointing exactly when we start relocating the fish in late March.

“By predicting the changes in oxygen levels in the water as it’s lowered, we can help manage fish health and reduce stress.

“At this stage, we’re planning to restock the reservoir with native fish, such as Golden Perch and Murray cod, in September 2023 to ensure the reservoir continues to be a popular destination among anglers.”

Warren Reservoir is expected to temporarily close to visitors for on-water access from mid-March, with a partial closure of the walking tracks in the reserve’s western section from April 2023.

Ms Lewry encouraged visitors to check out its more rugged neighbour during the temporary closure.

“South Para is only a short 15-minute drive from Warren and shares the same range of recreational activities, providing an excellent alternative for fishing,” Amanda said.

“We’ve also worked closely with Barossa Kayak Hire to move their equipment to South Para while there’s no access on the water at Warren, which is a wonderful outcome for visitors and keeps their business open.

“Emptying the reservoir for a short period is vital to performing the valve upgrade safely and efficiently, which ensures we can return it to full capacity as quickly as possible and have it open again to the public.”

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