New Zealand's world famous rainbow trout are tempting Kiwi and foreign fishing guides to operate outside the rules, according to the Professional Fishing Guides Association.

Professional fishing guides say illegal guiding is on the rise, and they are pressing for a compulsory guiding licence that would cut out rogue operators and relieve pressure on the freshwater fishery.

Searches of websites, Facebook and other advertising suggested more than 400 guides currently offered trips here, and it estimated about half of them were New Zealanders, the New Zealand Professional Fishing Guides Association (NZPFGA) said.

There was no way of knowing how many of the remainder were overseas guides working illegally, but the association was aware of cases where foreign guides pretended to be tourists, spokesman Craig Smith said.

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They lacked permits to legally work here or operate on Department of Conservation land, and did not have to meet the same standards as their Kiwi counterparts, such as having health and safety plans, a first aid certificate, and public liability insurance.

"It has got to a critical stage with the increase in tourism, and the grey area between someone conducting business within our borders for hire or reward, and the claim of hosting."

Kiwis were also breaking the rules by doing paid guiding without a DOC concession and claiming to be "hosting" friends or foreign anglers on rivers.

Smith said the worry was that an accident involving a client would sully the industry's reputation internationally, and there had been some very near misses such as a guide "losing a client" overnight.

"When a person gets a guide there's a reasonable expectation they're a professional, knows the waters well and is safe and legal in every respect, and these people aren't.

"We want to tidy it up and know who's doing what where. "

Smith said growing tourist numbers had also increased pressure on the fresh water fishery, particularly on back country rivers.

Fish & Game sales of fishing licences to non residents have risen steadily over the last three years from 4709 in 2014 to 6142 last year when there were 111,000 licences issued in total.

Smith said there were too many people going after a dwindling resource.

"We recognise this is not sustainable …we're very aware we cannot just keep guiding overseas anglers, we've got to get some checks and balances, and a guide's licence is a very simple compliance tool."

The NZPFGA plans to take up the licensing issue with Conservation Minister Eugenie Sage next month.

Chief executive of Fish & Game Martin Taylor said at present guides simply required a fishing licence.

Support for a separate professional fishing guide licence was still under consideration and would be decided by the Fish & Game board in the next six months.