What we're doing
Enlarged Cotter Dam – establishing artificial fish habitats in the Cotter
ACTEW Corporation is trialling artificial fish habitats in the Cotter Reservoir as part of the Enlarged Cotter Dam project. In partnership with ActewAGL, the University of Canberra and the ACT Government, this activity is a major component within a range of projects to facilitate the survival of threatened aquatic species which may be impacted by the new dam.
In 2007 ACTEW committed to increase the capacity of the Cotter Reservoir from 4 gigalitres (GL) to 78GL, as part of a suite of water security measures. Increasing the dam size will also mean increasing the deepest part of the reservoir by around 50 metres.
The greatest environmental concern is the potential effect of the construction and operation of the Enlarged Cotter Dam on threatened aquatic species. These include the Macquarie Perch, the Two-spined Blackfish, the Trout Cod and the Murray River Crayfish.
ACTEW must fully address 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.
ACTEW and ActewAGL have worked in close partnership with key stakeholders including the Environmental Protection Authority and ACT Territory and Municipal Services to ensure any environmental and water quality issues are addressed.
We have also engaged university researchers to provide a better understanding of potential risks to threatened species, including how to deal with such risks. Expertise has been provided by the University of Canberra, the Australian National University and the University of Sydney. The largest of the current projects being undertaken by the University of Canberra involves trialling artificial habitats for Macquarie Perch. The Macquarie Perch’s natural habitat, the existing macrophyte reed beds, will be lost when they are inundated by the enlarged reservoir.
In order to determine whether the Macquarie Perch will use artificial habitats in the absence of reed beds, researchers have installed a series of pilot artificial habitats made of rocks and/or pipes in the reservoir. By temporarily changing the water level in the reservoir, fish are denied access to the macrophyte reed beds. The researchers then track the threatened fish to assess whether they use the artificial habitats.
Monitoring of the fishes’ use of the artificial habitats has involved the use of underwater video photography and tracking of tagged fish. Early results of monitoring have been encouraging. Further analysis of a full four seasons of data will inform the most appropriate strategy for provision of artificial habitats.
The artificial habitat study mentioned above is one of a number of projects aimed at providing information for a comprehensive fish management strategy for aquatic species which may be affected by the Enlarged Cotter Dam. Other projects involve research into:
- food sources of threatened fish species;
- ensuring threatened fish can access spawning areas;
- assessing the presence of EHN virus in the existing reservoir;
- ecological requirements of the Murray River Crayfish;
- translocation of threatened fish species; and
- management of alien fish species.
ACTEW is also developing a monitoring program covering the potential impact of construction and operation of the new dam on threatened aquatic species.