Published on 28 August 2026
The Department of Conservation has approved a release of grass carp, also known as white amur (Ctenopharyngodon idella), to help manage overabundant native plant growth in the two stormwater lakes at Cooks Beach.
The Cooks Beach lakes systems are man-made lakes that form part of the Thames-Coromandel District Council’s stormwater network. In recent years, the lakes have experienced ongoing deterioration with increased aquatic plant growth, impacting the stormwater network. Various vegetation removal methods have been trialled and proved ineffective.
The release of grass carp follows years of lobbying from local residents and ratepayers to the Council for grass carp to help manage vegetation growth.
In August 2025, the Council applied to DOC for permission to release the fish and this month received approval for a period of three years. Grass carp is a restricted fish under the Conservation Act and is approved by the Government for use as a weed control agent with DOC consent.
The fish are used in New Zealand, and endorsed by the Ministry of Fisheries, as an alternative to mechanical draglines or herbicides. The Council previously used both mechanical weed harvesters and targeted herbicides at the lakes, but these were not effective.
The grass carp are not koi carp. They are a carefully managed, herbivorous fish that provide a cost-effective and environmentally focused option for long-term aquatic weed management.
Containment screens will be placed over the lakes’ outlets and spillways to prevent potential escape into the estuary. However, grass carp cannot survive in saline environments and do not reproduce in New Zealand waterways. Council expects to release the grass carp into the two lakes before Christmas.The Council is also carrying out riparian restoration around the lakes to also help further improve the water quality in the lakes.
Grass carp is used effectively in many locations across New Zealand, including Lake Kereta, Lake Tutirua and Lake Wainamu.