Background:
The Moira Lake wetland system is one of the most significant and largest wetlands in southern NSW. The Lake system is situated on the NSW-side of the Ramsar-listed Barmah-Millewa Forest. It consists of two shallow, open freshwater lakes, totalling an area of 1,500 hectares (ha), fringed by rushes and reeds, and surrounded by large areas of marshland and River Red Gum forest
Barmah Millewa Forest. Major wetland areas shaded blue
The Moira Lake system provides a range of vegetation and wetland types due to slight variations in elevation across the floodplain and resulting in differences in the frequency and depth of inundation. These include areas consist of reedbeds, open rush and grass plains and River Red Gum forest.
Prior to the construction of Hume Dam, Moira Lake supported large waterbird breeding colonies and was a major native fish breeding site for the central Murray region, particularly for Murray Cod. However, following the completion of the Hume Dam in 1936 the frequency, extent and duration of winter and spring flood events declined, and regular periodic drying in summer and autumn no longer occurred. These changes altered the ecology of the lake, reducing its ability to support many native plants and animal species whose lifestyles depended on flooding and drying, which in turn created ideal conditions for pest species such as carp and native opportunist species such as Giant Rush (Juncus ingens).
Graph illustrating changes in the frequency of drying at Moira Lake due to river regulation.
(Graph sourced from the Wetlands of the Barmah-Millewa Forests)
Rehabilitation Project:
The NSW Murray Wetlands Working Group, in conjunction with NSW State Forests and the Department of Infrastructure Planning and Natural Resources (former Dept. of Land and Water Conservation) have developed a rehabilitation plan for the wetland system aimed at counter-acting the impacts of river regulation.
The first two stages of the plan have been completed. This included the engineering works of constructing and installing a regulator, which excludes regulated river flows from Moira Lake during summer. These works have allowed the Lake to dry over the summer of 1997/98 the first time in 60 years, as well as in 1998/99 and 1999/00. .
Re-establishment of the natural cycle of drying and re-flooding will gradually restore native fish and waterbird habitats throughout the wetlands. The exclusions of summer flows has the additional benefits of improving the efficiency of water supply down the river by reducing the evaporative losses from the Lake, estimated to be 2,027 megalitres (ML).
Installation of Moira Lake regulator. (Photo courtesy of David Leslie)
Stage 3 of the rehabilitation plan has been designed to:
- Allow the Moira Lake to drain back to the Murray River during periods of regulated flow;
- Improve the movement of native fish between the Murray River and the wetlands by providing fish passage; and
- Maintain the productivity of nearby swamp meadows.
Royal Spoonbills nesting in Reed Beds Swamp, Moira State Forest. (Photo courtesy of David Leslie).
Environmental Flows:
Provision of environmental flows, piggy-backed onto natural floodwaters, to the Barmah-Millewa Forest in 2000/01 saw the return of large waterbird breeding colonies along the shores of the Moira Lake. Up to 30,000 birds successfully bred in the wetlands including species such as the threatened brown bittern, great and intermediate egrets, black swans, nankeen night herons, comorants and ibis. Some of the bird species recorded during the breeding event had not been seen in the area for more than 30 years.
Carp Harvesting:
After flooding the wetlands, carp harvests are conducted as water drains back from the wetlands into the Murray River. A specially designed net has been used to catch the carp. The net's mesh size is large enough for smaller native fish such as Australian smelt to pass through freely and there has been no evidence of the net injuring larger native species such as Murray cod. A commercial fisher is employed to conduct the harvest, and convert the carp into a popular garden fertiliser.
In 2001 approximately 80 tonne of Common Carp (Cyprinus carpio) was captured before returning into the Murray River. In 2004 up to 40 tonne of carp was harvested from the wetlands.
Through point-source control of carp such as is in Moira Lake, can help keep in check and even reduce carp numbers. This will help lead to good environmental outcomes for wetlands, rivers, and native fish.
Future Management and Research:
A range of management actions including engineering works, environmental flows, fencing to exclude stock from the Lake and carp harvesting will continue to improve Moira Lake and its wetlands. The latest management tool to be trialed is the use of fire to manage the beds of Giant Rush.
A range of research projects are being undertaken to monitor and assess changes to fish, vegetation, waterbirds and micro-invertebrate assemblages within the wetlands. Organisations involved include NSW Fisheries, Monash University, the CRC for Freshwater Ecology and the Barmah-Millewa Forum.
Moira Lake - Full (winter/spring)
|
|
Draw Down (Late Spring)
|
|
|
|
Moira Lake - Dry (Summer/Autumn)
|
|
Carp Harvesting (during draw down)
|
| 
