Protecting native fish species

The Cotter Reservoir was enlarged in 2013 to improve water security following the millennium drought.  

It reservoir contains the only self-sustaining ACT population of the nationally endangered Macquarie perch, Macquaria australasica, one of only a few populations in southeastern Australia. Working closely with experts from the University of Canberra, Australian National University and University of Sydney, Icon Water has developed a comprehensive program to protect this threatened aquatic species. 

Macquarie perch require flowing water to spawn, as they lay their eggs in runs and riffles where the flowing water keeps the eggs oxygenated and clear of sediment. 

While constructing the enlarged Cotter Dam, Icon Water established artificial fish habitats - specially constructed habitat reefs to provide artificial shelter habitat for the Macquarie Perch until the reservoir filled and new natural habitat was established. Research continues to be conducted by the University of Canberra (Institute for Applied Ecology) and Icon Water, in consultation with catchment land managers and regulators, to address key risks during the filling and operational phases of the reservoir. 

On ground works have included the physical modification of barriers and construction of fish passages, review of environmental flow releases and a comprehensive fish monitoring program. 

An acoustic monitoring program and spawning site characterisation research have helped to determine the timing and extent of Macquarie perch movements in the spawning seasons since 2016. These studies discovered that the vast majority of spawning migration by the fish occurs at night (between 5–6pm) and spawning is closely related to rises in water temperature over 16°C. 

These research findings are world leading and have broad implications for management of inland reservoirs and rivers with native fish populations.  

The existing Cotter Reservoir and Cotter River provide critical habitat for several other aquatic species too, including: 

  Macquarie Perch (Macquaria australasica)
  Endangered (the only sustainable ACT population is in the Cotter Reservoir)


  Trout Cod (Maccullochella macquariensis)
  Endangered

  Murray Cod (Maccullochella peelii peelii)
  Vulnerable

  Two-spinned Blackfish (Gadopsis bispinosus)
  Vulnerable

  Murray River Crayfish (Euastacus armatus)
  Vulnerable

Icon Water is committed to addressing issues which may impact on these threatened species in order to comply with the requirements of the ACT’s Nature Conservation Act and the Federal Government’s Environment Protection and Biodiversity Conservation legislation.

Establishing artificial fish habitats

When the Enlarged Cotter Dam was completed and the reservoir began to fill, the macrophyte reed beds that Macquarie Perch used as shelter were be inundated. As part of a comprehensive fish management program involving Icon Water and the University of Canberra, Australian National University and the University of Sydney, Icon Water completed a trial of artificial fish habitats for the endangered Macquarie Perch population in the Cotter Reservoir. Results showed that in the absence of reed beds Macquarie Perch prefer artificial rock reefs over other forms of artificial habitat that were trialled.

Following the submission of a Development Application to the ACT Planning and Land Authority in early 2011, work began on constructing artificial rock reef habitats at carefully selected sites around the Cotter Reservoir for the Macquarie Perch.

Fish habitats

The rock reef habitats taking shape at the site

Managing risk to aquatic species

A series of studies are being undertaken by various government agencies, university researchers and Icon Water to mitigate potential risks associated with the construction and later operation of the Enlarged Cotter Dam. Results from these studies will enable Icon Water to understand and manage:

  • use of artificial habitats by Macquarie Perch;
  • the impact of fluctuating reservoir levels on Macquarie Perch food sources;
  • the possible recolonisation of the enlarged Cotter Reservoir by Two-spined Blackfish;
  • the ecology and habitat preferences of Murray River Crayfish;
  • measures to protect the Cotter Reservoir from the EHN virus (fatal to some threatened native fish species);
  • native fish access to upstream sections of the Cotter River;
  • establishing other populations of Macquarie Perch and Two-spined Blackfish in locations outside the Cotter River system;
  • the impact of alien fish species on threatened native fish populations;
  • monitoring and evaluation as the basis for adaptive management measures to protect threatened species from predators and competitors within the enlarged Cotter Reservoir.

Icon Water continues to work with our partners to help protect these fish species, and these activities remain integral to the ongoing Enlarged Cotter Dam works.