Freshwater anglers are being asked to keep an eye out for pest species after a grass carp was caught in an Otago lake.

It is believed the carp was released into contained ponds near Queenstown, but may have escaped during spring floods and swum down river into Lake Dunstan, Otago Fish and Game said.

Central Otago operations manager David Priest said it was important for any pest fish species to be reported to Fish and Game to protect valuable fisheries.

"We appreciate the angler notifying us of this unexpected catch. Any further sightings of grass carp in Otago waterways should be reported.

"Thousands of anglers have been enjoying fishing for trout these summer holidays and harvesting wild kai from our Southern Lakes fisheries.

"The last thing we want is a disease entering highly valued fisheries," he said.

Grass carp could not readily breed in New Zealand outside of captivity so there was no real risk of establishing a self-sustaining population in the wild, Priest said.

They are a herbivorous fish native to Asia, that weigh 10kg and commonly grow more than half a metre in length.

Grass carp are artificially bred and grown on fish farms licensed by the Ministry for Primary Industries and have been used in parts of the country to control aquatic weed growth.

But, a permit was required to move grass carp and they had to be contained in the water body where they were released.

Priest said one of the major concerns over the use of grass carp in New Zealand was their potential effect on trout fisheries in lakes.

"Grass carp released into contained waters had the potential to host infection and disease, which could then be carried and transferred to other waters or species."

The fish species have been released in a wide range of locations in the North Island but their distribution was more limited in the south.

MPI most recently authorised the release of 100 grass carp to artificial ornamental ponds near Queenstown in February last year.

They have been used for aquatic weed control in a select number of contained ponds in the area since 2013.