Fish die-offs due to water deoxidising in the Whangamarino wetland
Image: Matthew Brady | DOC


Koi carp contribute to poor water quality and are a serious problem in both Australia and New Zealand.

Koi carp look very like goldfish, except they grow to larger sizes (in New Zealand up to 10 kg and 75 cm long) and have two pairs of whisker-like feelers, also called barbels, at the corners of their mouth.

They are highly variable in colour, often accompanied with irregular blotching of black, red, gold, orange or pearly white.

Koi carp prefer still waters in lakes, or backwaters in rivers. They are highly tolerant of poor water quality and contribute to water quality decline.


In this section

Koi carp are an ornamental strain of the common carp (Cyprinus carpio) native to Asia and Europe. This species is thought to have been imported into New Zealand accidentally in the 1960s as part of a goldfish consignment.

Wild stocks of koi carp were first found in the Waikato River in 1983, by which time they had likely established a breeding population and begun to spread naturally, during floods and accidentally or intentionally by people.

Further illegal introductions have occurred elsewhere, for coarse fishing (a traditional British pastime involving the catch and release of certain species including koi carp, rudd, perch and tench) and for ornamental purposes. Isolated populations have been progressively discovered throughout the North Island .

What damage do they do?

When koi carp feed they stir up the bottom of ponds, lakes and rivers, muddying the water and destroying native plant and fish habitat. Koi carp are opportunistic omnivores, eating a wide range of food, including insects, fish eggs, juvenile fish of other species and a diverse range of plants and other organic matter.

They feed like a vacuum cleaner, sucking up everything and blowing out what isn’t wanted. Aquatic plants are dislodged in the process and are unlikely to re-establish. Koi carp cause habitat loss for plants, native fish, invertebrates and waterfowl. They can also worsen river erosion by undermining banks as they feed.

 Legal designation

  • Unwanted Organism
  • Noxious fish

It is an offence to sell, breed or distribute any Unwanted Organism under Sections 52 and 53 of the Biosecurity Act 1993. Moving live koi carp is also an offence. Penalties include a fine of up to $100,000 and/or imprisonment up to 5 years (Section 157 (1)).

People who possess, control, rear, raise, hatch or consign Noxious Fish without authority are liable for a fine of $5,000 under the Freshwater Fisheries Regulations 1983.

Under Section 26ZM of the Conservation Act 1987, any person who transfers or releases live aquatic life into any freshwater without  prior approval commits an offence and is liable for a fine of up to $5,000.

What’s being done to control koi carp

Containment area – Auckland and Hamilton

To help stop their spread, a containment area between Auckland and Hamilton was established in 1990.

Map of the containment area (PDF, 104K)

The commercial harvest of koi carp can take place from waters within the koi carp containment area but you will need approval. See Harvesting koi carp

Recreational fishing is permitted, but all koi must be killed when caught.

Koi are widespread in Northland, Auckland and the Waikato River catchment downstream of Lake Arapuni.  They are now found in the Waihou and Piako Rivers. They are also located in isolated places throughout the North Island except East Cape/Gisborne.

There are no known populations of koi carp in the South Island.

Removal of koi from outside the containment area

Koi carp outside of the containment area are considered a serious pest and control options will be investigated, particularly in cases of small and isolated populations of the fish. If you catch or spot a koi carp outside the known geographical extent of the species you should report this or any other sighting to the DOC hotline, 0800 DOC HOT (0800 362 468).

Koi carp have been eradicated from small sites throughout the North Island. Illegal releases of koi carp in the Nelson/Marlborough area in 2000 were eradicated.  

Preventing the spread

Check, Clean, Dry methods for all water users

DOC is a member of the Freshwater Biosecurity Partnership Programme, led by Biosecurity New Zealand (part of the Ministry for Primary Industries). This collaborative programme was established in 2007 to target didymo but was expanded in 2016 to include all freshwater pests.

The programme supports a multi-organisation partnership to help prevent the spread of freshwater pests (not just fish) through coordinating work primarily focused on advocacy and pathway management.  Advocacy aims to change behaviour around waterways to prevent the unintentional spread of freshwater pests.

It does not have a specific programme focusing on koi carp, however the MPI websites provide cleaning guidelines for water users that are effective across a range of freshwater pests.

Check, Clean Dry measures on the MPI website

Active and passive surveillance

Early detection of new koi sites increases the chances of successfully eradicating them. Planned or active surveillance programmes for pest fish, including koi carp, are conducted by DOC either alone or alongside some regional councils.

A variety of tools and methods are used in surveillance, including environmental DNA (eDNA), where water samples are analysed for genetic material of plant and animal species present in a waterway.

Passive surveillance relies on members of the public reporting any sightings of koi carp. Reports are responded to by DOC and/or regional councils. If you find koi outside of the containment area report it to 0800 DOC HOT (0800 362 468).

Regional pest management plans

The Biosecurity Act 1993 enables the establishment of regional pest management plans and pathway management plans by regional councils and these can also help reduce the spread of pests like koi. DOC has a role in working with individual regional councils in developing these plans and establishing appropriate regional controls.

Control options

Controlling koi is limited by the small range of tools available and the ability of those those tools to make real impacts on the koi carp population. Although the eradication of koi is highly desirable, it is a challenging goal.

It has taken millions of dollars and 25 years of consistent effort for Tasmania to eradicate carp from an enclosed lake, screening the lake outlet to prevent any fish from entering or leaving the lake, and using multiple methods of physical removal. In New Zealand, koi carp have only been eradicated from small ponds that are hydrologically separate from other water bodies.

Existing tools to control koi include manual removal using nets, traps, electric fishing or recreational fishing, and draining the water body, the use of toxins and selective barriers.  These are generally not effective on their own and need to be used in combinations suiting each situation. 

Most of the tools are only effective in enclosed/isolated and/or non-flowing water bodies and would not work in an open catchment system, such as a river. None of the existing control tools can specifically target koi, so their use needs to be considered carefully with regard to potential impacts on New Zealand’s native species

Current work programmes are focussed on exploring new and innovative control tools. This includes drone and eDNA surveillance and commencing a project for a species-specific virus.

Koi carp control tools -  what's currently available and new tools being explored.

DOC’s Biodiversity 2018 programme

This programme has $2.1 million allocated specifically to targeting freshwater biosecurity and now has an enhanced national programme focussing on priority freshwater pest plants and pest fish nationally.

The funding has enabled the establishment of new positions in freshwater biosecurity to increase staff numbers, has supported a range of eradication programmes and funded research projects to identify new monitoring, surveillance and potential control tools.

Waikato Freshwater Pest Programme

DOC and Waikato Regional Council have established an agreement to work together to manage freshwater pests, including koi.  Although this agreement targets the Waikato region, the programme is linked with stakeholders across New Zealand with similar pest fish issues. 

The agreement includes a Waikato coordinator role to drive the regional programme of work, maintain oversight across pest fish issues regionally and nationally and also pull resources together for future control programmes.

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