Many changes to the condition of the Lachlan River have contributed to the degradation of native fish habitat. River regulation has changed the flow conditions upon which many native fish depend. Changed flow patterns and degraded riparian zones increase bank erosion and turbidity and sedimentation within channels, filling pools and smothering habitats, including macrophytes, woody debris and gravel substrates (MDBC 2003).
Constant mid to low flows reduce ecosystem productivity by removing the boom (wet) and bust (dry) cues that trigger and sustain aquatic cycling. Other threats include increased runoff of contaminants into receiving waters, competition with introduced species, and structures in the river that act as barriers to movement (MDBC 2003). Some structures have been found to threaten fish directly. Fish larvae are usually poor swimmers, and travel with currents and researchers suggest that larval and juvenile fish are directly extracted from the river through pumping for irrigation and town supply. Weirs with an undershot design are also known to cause high mortality in larval and juvenile fish, for example, 95% of golden perch have been found to die after passing through undershot weirs (Baumgartner et al. 2006; DPI 2007). Releases of cold, poor quality water from the bottom of Wyangala Dam may also adversely affect aquatic habitat for many kilometres downstream (Burton and Raisin 2001).
Many changes to the condition of the Lachlan River have contributed to the degradation of native fish habitat. River regulation has changed the flow conditions upon which many native fish depend. Changed flow patterns and degraded riparian zones increase bank erosion and turbidity and sedimentation within channels, filling pools and smothering habitats, including macrophytes, woody debris and gravel substrates (MDBC 2003).
Constant mid to low flows reduce ecosystem productivity by removing the boom (wet) and bust (dry) cues that trigger and sustain aquatic cycling. Other threats include increased runoff of contaminants into receiving waters, competition with introduced species, and structures in the river that act as barriers to movement (MDBC 2003). Some structures have been found to threaten fish directly. Fish larvae are usually poor swimmers, and travel with currents and researchers suggest that larval and juvenile fish are directly extracted from the river through pumping for irrigation and town supply. Weirs with an undershot design are also known to cause high mortality in larval and juvenile fish, for example, 95% of golden perch have been found to die after passing through undershot weirs (Baumgartner et al. 2006; DPI 2007). Releases of cold, poor quality water from the bottom of Wyangala Dam may also adversely affect aquatic habitat for many kilometres downstream (Burton and Raisin 2001).