A fish passageway that lets fish swim upstream out of the Menindee weir pool into the Menindee Lakes in western New South Wales has reopened for the final season of its three-year trial, as low water and poor water quality raise fears of another fish kill in the Darling-Baaka River this summer.

The passageway, operated by the Finnish company Fishheart, is expected to carry up to 50,000 fish between now and late May or early June. It was installed to reduce the risk of mass fish kills such as the 2023 event, in which about 30 million fish died in the area.

Cameras inside the passage photograph fish as they travel through, and regular upgrades to the cameras, the lighting and the artificial-intelligence software have improved the system's ability to identify them. Fishheart co-founder Mika Sohlberg said numbers had grown as the company came to understand the river better: "The first season we got 7,000 fish, and then around 30,000 fish." The company regularly consults a local group of traditional owners on fish behaviour.

The fishway reopens with the Menindee Lakes at a combined 29 per cent of capacity, low rainfall in the catchment and algal bloom alerts in parts of the lakes. Cameron Lay, director of Freshwater Fisheries and Threatened Species at the NSW Department of Primary Industries and Regional Development, said the passage lets fish leave the weir pool, where many had died because food and oxygen ran short as they gathered there.

Lay said blue-green algae was a concern although oxygen levels were generally fine, and that the biggest worry was a hot, dry summer with El Niño developing: "Things can change very quickly when you get extended periods of 40-degree days."

Whether the fishway will continue after the trial has not been confirmed. Lay said it was only one part of the work needed to improve river health, and that outcomes of the Basin Plan Review, due in December, would then begin to be implemented; the review panel heard that investment should go beyond buying back water. The report was written by Em Jensen of ABC Broken Hill.

Photo: Jeremy Buckingham / Wikimedia Commons (CC BY 2.0)

Source: ABC Rural