Boaties on Lake Rotorua are being urged to clean their gear after the discovery of the aquatic pest catfish.

Six were caught near Mokoia Island just prior to Christmas.

Bay of Plenty Regional Council is asking boaties to remove all weeds from boats and trailers and empty out any water they may be carrying.

It said the request was relevant to water-skiing and wakeboarding as well.

Biosecurity manager Greg Corbett says while catfish had been in Lake Rotoiti since 2016, finding them now in Lake Rotorua was devastating.

"They predate on native species such as koura and bullies and the ability to predate on young trout and trout eggs."

Greg says a single catfish could lay up to 10,000 eggs.

He says once established it was near-impossible to eradicate them especially in the size of the Rotorua lakes.

"To our knowledge eradication has never been achieved anywhere in the world to date."

He says the methods being used were quite primitive.

"Using nets and while we are able to catch relatively large numbers it is difficult to catch enough of them to limit their populations."

It is not known how catfish got into Lake Rotorua but it is likely they did by moving through the Ōhau Channel.

Catfish were first introduced into New Zealand from North America in the late 1800s.

He says catfish were easy to identify.

"They are a dirty brownie green colour and distinctive with whiskers around their mouths, with a spine on their dorsal and pectoral fins which are painful if touched.

"They will make them say ouch!"

They can survive in extreme conditions, including being out of the water for up to 48 hours in summer.

-RNZ