Environmental water is delivered throughout the Murray–Darling Basin to restore ecological processes, including the long-distance fish migrations that underpin recruitment of native fish—a key objective of the Basin Plan. However, these outcomes depend on fish being able to move through a connected river network. Mildura Weir, immediately upstream of the Darling River confluence, is a critical passage point linking the lower Murray and Darling rivers—major recruitment areas for Golden Perch—to upstream habitats in Victoria and New South Wales. Previous assessments suggest fish passage at this site is poor.
This presentation summarises the outcomes of a trial investigating two alternative fishway entrance configurations and targeted manipulation of fishway attraction flow at Mildura Weir. Fishway exit trapping was used to compare new vertical-slot and extended wing-wall entrances against the original design. Attraction flows were refined daily using expert assessment of hydraulic conditions and manipulation of weir drop boards, while acoustic telemetry was used to investigate fish behaviour downstream of the weir.
Up to 400 Golden Perch per day were recorded passing through the fishway, with peak passage linked to elevated river flows and optimised attraction flows. The denil entrance with an extended wing-wall was particularly effective during periods of high tailwater, when turbulence at the entrance could not be adequately managed through attraction flow adjustments alone. However, acoustic telemetry indicated low overall passage success, with only three of 60 tagged fish successfully passing the weir, including one via the navigation lock.
These results demonstrate that fishway performance at Mildura Weir is strongly influenced by hydraulic conditions and entrance configuration but also confirm that the weir remains a major bottleneck to basin-scale migration. Improving fish passage at this site may represent one of the greatest opportunities to increase the ecological return on environmental water delivered for Golden Perch across the Murray–Darling Basin.