Moira Lake Wetland System - Rehabilitation Project

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.

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 reed beds, open rush, 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).

Rehabilitation Project:

The former NSW Murray Wetlands Working Group, in conjunction with NSW State Forests and the former Department of Infrastructure, Planning and Natural Resources, 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 1997-1998, the first time in 60 years, as well as in 1998-1999 and 1999-2000.

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).

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.
  • Maintain the productivity of nearby swamp meadows.

Environmental Flows:

Provision of environmental flows, piggy-backed onto natural floodwaters to the Barmah-Millewa Forest in 2000-2001 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, cormorants 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 drained back from the wetlands into the Murray River. A specially designed net was used to catch the carp. The net's mesh size was large enough for smaller native fish, such as Australian smelt, to pass through freely and there were was no evidence of the net injuring larger native species, such as Murray cod. A commercial fisher was 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.

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 trialled was the use of fire to manage the beds of Giant Rush.