Grass carp released into Cooks Beach lakes

In a 5 November press release the Thames Coromandel District Council reported the following:

The Cooks Beach lakes are man-made and form part of the council’s stormwater network. In recent years, increased aquatic plant growth caused ongoing deterioration, affecting the network and leaving the lakes unsightly with an unpleasant smell. 

Cooks Beach residents and ratepayers have long lobbied for the grass carp to help clear the plant growth.  
Previously, attempts at managing the plant growth with weed harvesters and herbicides were unsuccessful. 
Because the grass carp are a restricted fish under the Conservation Act, they can only be used as a weed control agent with a DOC consent. In August 2025, Council applied to DOC for consent and received approval in August 2026 for a period of three years.  

Council Water Services Manager Brett Houston says it has been a long process to get to this point, but it is good news the grass carp have now arrived.  “It has taken a lot of time, care and patience from the community for us to finally reach the point of releasing the grass carp, which we hope will provide a sustainable and safe way to help manage the lakes.” 

Mr Houston says it is important to note that grass carp are not koi carp. They are a carefully managed, herbivorous fish that cannot survive in saline environments. 

Grass carp are already used successfully at other New Zealand lakes, including Lake Kereta, Lake Tutirua and Lake Wainamu, and are endorsed by the Ministry of Fisheries as an alternative to mechanical draglines or herbicides. They offer a cost-effective, environmentally focused option for long-term aquatic plant growth management. 

Council report that residents shouldn’t expect the plant growth to disappear overnight. The fish feed more actively as the water warms, so the difference should become more noticeable over the coming months.