Kapiti takes aim at ‘possums of freshwater’

Source: NZ Department of Conservation

Date:  01 April 2026

The Department of Conservation (DOC) has partnered with mana whenua to eradicate introduced koi carp from stormwater retention ponds on private land in Paraparaumu.

DOC Freshwater Technical Advisor Phoenix Hale says koi carp are “an absolute menace” to freshwater plants and animals, outcompeting them for food, preying upon native invertebrates, and churning up sediment.

“Although we only know of a few remaining koi carp populations in the lower and eastern North Island, they breed like crazy and could easily spread further. They’re like the possums of freshwater.”

DOC, partners, and the landowners planned the eradication project following landowners’ reports of koi carp in the stormwater retention ponds several years ago.

“We attempted to remove koi carp by draining the ponds last year, but excessive rainfall refilled them before we could get to the fish,” Phoenix says.

“Our plan then changed to using rotenone, a plant extract that’s toxic to fish, which is the most effective koi carp control tool we’ve got.”

The koi carp eradication using rotenone took place in March 2026, following a massive translocation effort where DOC moved more than 21,000 native fish from the stormwater ponds to safe waterways nearby.

The eradication team is monitoring the ponds closely to make sure all the koi carp were removed. To confirm the eradication was successful, the site must be carp-free for three years.

Northland Regional Council and Greater Wellington Regional Council supported DOC and mana whenua with the eradication operation. Northland Regional Council staff travelled to Kapiti to lend a hand and learn more about how to run a rotenone operation.

DOC led an eradication of a Dannevirke koi carp population last year, and all signs point to it being successful, though final results are still a couple of years away.

Phoenix says there is another suspected koi carp population is in Lake Waitawa, also in the Kapiti area.

“Waitawa is a large lake and a popular spot for recreation, so an eradication operation would be complex. Any work on koi carp at this site would be done in close collaboration with the landowners, Fish & Game, and mana whenua.”

DOC is asking for the public’s help to eradicate koi carp from the lower North Island. If you see a koi carp – they’re large orange fish with a ‘moustache’ – do your bit for naturing and call 0800 ASK DOC (0800 275 362) to report it.

For more information on koi carp

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