Some impacts of low and medium head weirs on downstream fish movement in the Murray-Darling Basin in southeastern Australia

This article reports on the findings of a study undertaken within the Murray-Darling River Basin in southeastern Australia, which investigated the impact of weirs on downstream fish movement. Downstream fish movement was monitored at Kennedy's Weir (an overshot, 2 m high weir) on the Broken Creek and Torrumbarry Weir (an undershot, 6.5 m high weir) on the Murray River. A trap used to sample Kennedy's Weir indicated that fish travelled downstream over this weir without sustaining injury or death. A follow-up study, whereby fish were captured below the two respective weirs and translocated upstream where they were radio tagged and released, indicated that while a few fish travelled downstream past the weirs on their return movements back to their home range areas, most were reluctant to do so. This study demonstrates that low-level weirs may inhibit downstream fish movement, and enhancement of downstream fish passage for potamodromous fish species warrants further investigation.