Cold water pollution is a significant problem hindering the recovery of native fish populations in the Murray-Darling Basin (MDB). Despite this, the extent and effects of cold water pollution is largely unknown for many catchments in the MDB. The objective of this project was to scope the feasibility of a four year impact assessment investigating the response of the fish community in cold water pollution affected reaches of the Namoi River to the operation of a multi-level offtake at Keepit Dam.

A further goal of a full impact study would be to use the resulting knowledge to estimate the likely long-term recovery of the fish assemblage and provide information to assist in the rehabilitation of other riverine habitats throughout the MDB affected by cold water pollution.

Findings:

The results of the scoping study led to five conclusions:

  1. more extensive cold water pollution mitigation research is needed in the MDB.
  2. there is a need to monitor the effects of cold water pollution mitigation using a MBACI (Before and after, control and impact, and at multiple sites) study design.
  3. the monitoring budget is disproportional for the Keepit Dam cold water pollution mitigation works.
  4. poor likelihood of detecting an impact at Keepit Dam (at best the mitigation would result in only a 5 degree change).
  5. climatic conditions at the time of the study not conducive to doing the proposed research (drought conditions imposed by El Nino)
Keepit Dam arial showing Cofferdam

Implications:

This scoping study highlights the importance of monitoring the effects of cold water pollution on the native fish species of the MDB. It presents a robust method by which to determine these effects that could be used at various locations into the future. Better management and mitigation of cold water pollution in the MDB will result in a range of benefits to native fish such as providing appropriate spawning cues, increased food availability and growth of early life stages of native fish.

Read the full report here:  Boys, C. A., Miles, N. & Rayner, T. 2007. Scoping options for assessing the impact of cold water pollution mitigation on the fish assemblage downstream of Keepit Dam, Namoi River. NSW Department of Primary Industries, Port Stephens.

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