MAFBNZ to use fish to eradicate invasive aquatic weed from lakes

The Ministry of Agriculture and Forestry Biosecurity New Zealand (MAFBNZ) is releasing 3000 grass carp into Lakes Tutira, Waikopiro, and Opouahi today as part of its programme to eradicate the invasive aquatic weed hydrilla from the lakes. Hydrilla has not been found anywhere else in New Zealand.

Grass carp (also known as white amur) graze on aquatic vegetation and have been used successfully to eliminate hydrilla in Lake Eland in Hawke’s Bay.

“They are the only method of biological control known to be successful for hydrilla eradication or the large scale control of weed beds,” said MAFBNZ Senior Adviser, Pest Management, Victoria Lamb.

“Scientists estimate that the hydrilla weed beds should begin to reduce in size about eighteen months after grass carp are introduced into the lakes. The weed beds should disappear completely within three to four years following the release of the grass carp.”

Victoria Lamb said grass carp were bred especially for the purpose. “They cannot breed naturally in New Zealand waterways, so they can be removed or will naturally die-out once they have done their job.”

“Barriers to prevent the movement of grass carp from Lake Waikopiro and from Lake Tutira will be placed between the lakes and at the outlet of Lake Tutira. This will ensure that the fish remain in their allotted lakes to maintain the grazing pressure on the hydrilla,” said Victoria Lamb.

MAFBNZ commissioned the National Institute of Water and Atmospheric Research (NIWA) to prepare an Assessment of Environmental Effects report for grass carp. The assessment found that the removal of the hydrilla will allow native aquatic plants to regenerate with minor effects on the water quality and fisheries of the lake.

Approval to release the carp into the lakes has been granted by the Department of Conservation and Fish and Game, and has support from Hawke’s Bay Regional Council and local iwi.

Hydrilla was first detected in Lakes Tutira and Waikopiro in 1963 and later found in Lakes Opouahi and Eland. Weed beds of hydrilla are a nuisance to lake users such as bathers, anglers and boat users. Plant material washed ashore rots, reducing the aesthetic value of the lakes, and restricting access to water. It can also clog hydroelectric dams and block water intakes in water bodies where it is present, costing millions of dollars each year to clean up.


For more information about the hydrilla eradication response for Lakes Tutira, Waikopiro and Lake Opouahi go to the hydrilla pages on the pests and diseases section of the MAFBNZ website www.biosecurity.govt.nz.

Propagation, spread and sale of hydrilla is prohibited under the Biosecurity Act 1993. All suspected sightings must be reported to MAFBNZ on 0800 80 99 66.

Hydrilla is one of 11 established pests of national interest MAFBNZ aims to eradicate or control in New Zealand. These pests were selected for a national response because of their potential to have a significant impact on our economic, environmental, social and cultural values.