Too close for comfort : a fishway exit and a hydro-power station inlet

A major environmental issue for hydro-electric power generation is passage of fish through turbines, or entrainment onto trash racks. At Yarrawonga Weir, on the upper Murray River in south-eastern Australia, the positioning of a fish lock resulted in the potential for upstream migrating fish to be swept back into the adjacent power station by cross flows. In 2004, a 4.5-m long steel extension flume was attached to the exit to alleviate this problem. To determine the fate of native fish after exiting the extension flume, 72 individuals (305–1015 mm long) were implanted with radio-transmitters and released into the fish lock exit channel. In 2004 (power station inflows 10 300 ML day^–1), the majority of fish exited successfully (44 of 45) and only a single fish (2%) was entrained into the power station. In 2005 (power station inflows 12 000 ML day^–1), fish again exited successfully (26 of 27) but with a higher proportion entrained (5 of 27; 18%). This reduced success appeared to be related to strong transverse flows with high water velocities adjacent to the fish lock exit. The efficiency of fish passage at this site might be improved by altering water management strategies, integrating engineering and fish biology, and through field-testing of proposed solutions