Koi Carp Barrier at Lake Ruatuna

Koi Carp Barrier at Lake Ruatuna

Fish Habitat – With Descriptor

About the project

Extensive pest fish netting, boat electric fishing and eDNA investigations show there are no Koi Carp detected in Lake Ruatuna. Because of their destructive nature, preventing them from entering the lake is a high priority.

Koi carp (Cyprinus carpo) are native to Asia and Europe and look similar to goldfish. Their colouring is highly variable – gold, black, red, orange and pearly white and have whiskers at the corners of their mouth (they can grow as large as 10 kg and 75 cm long)! They are widespread in other parts of the Waikato, Auckland and Northland regions, and in isolated populations throughout the North Island. There are no known populations in the South Island. 

It's important we stop them from spreading further because of the harm they cause to our freshwater ecosystems. As there is limited ability to control koi carp, this barrier is a tool in a toolbox of various options that used together are most likely to be effective (more about options here). Koi carp are very hard to eradicate and highly destructive.

Dion Patterson

Dion Patterson

DOC Site Lead, Waikato Peat Lakes and Pūkorokoro-Miranda
Rose Graham

Rose Graham

DOC Ranger - Waikato Peat Lakes and Pūkorokoro-Miranda
Koi Carp Barrier


  • Designed by Gumbley Ecological Consultancy and Daniel Hall Engineering November 2018
  • Consultation with landowner and Council Drainage December 2019
  • Iwi and stakeholder consultation March 2020
  • RMA Consent Application April 2020
  • Construction Daniel Hall Engineering March 2021
  • Installation completed May 2021


  • Koi carp are devastating to our freshwater environments, they feed like a vacuum cleaner, sucking up anything in their wake and blowing out anything they don't eat - which isn't much. They eat insects, fish eggs, small fish, plants and almost any other organic matter. Their manic feeding stirs up the bottom of waterways, further degrading water quality which destroys habitat for our native fish but Koi carp can happily live in degraded water
  • A female koi can lay half a million eggs at a time so prevention preferable to trying to control the population.

What's Next

The barrier will be checked regularly for blockages and possible weed clearance.  Maintenance will be scheduled as part of regular predator trapping lines DOC Rangers and volunteers do around the lake.

Theo Bongers and Koi Carp Barrier