Freshwater fishing is a big drawcard for tourism in New Zealand.
But some in the industry have serious concerns about its future, including claims that two-thirds of fishing guides are operating illegally.
"Sixty-six per cent of the guides we surveyed are fishing in illegal manners in New Zealand," NZ Professional Fishing Guides Association president Serge Bonnafoux told 1 NEWS.
The association says over five years it has questioned 541 people who advertised guiding services.
"The reputation of the industry can be just put at risk because of people who are not doing things legally," Mr Bonnafoux said.
Fly fishing guide Tony Entwistle has been guiding for 38 years and ensures he meets the standards of the association.
"We're all first aid qualified, every two years. We're governed by a very stringent health and safety system. We have to have a Department of Conservation concession for those administering services on public land. We have commercial vehicle insurance, we have public liability insurance," Mr Entwistle said.
"We always knew that there were more than the 150 members of the NZPFGA, but 500 people plus guiding would indicate to me that the resource isn't going to last very long."
The survey also found that 10 per cent of those advertising guiding services here weren't based in New Zealand.
In a statement, the Department of Conservation said it's not aware of a growing trend of tourists working illegally as guides on public land.
"The issue of licences has come up in the past but at the time there wasn't enough evidence to justify taking any action," DOC said.
The NZ Professional Fishing Guides Association wouldn't release its full research findings to 1 NEWS. Instead it says it'll be taking the results to Conservation Minister Eugenie Sage, with a plea for strict regulation.
"We started pushing for a guides license in 1987 when the Conservation Act first came into being," Mr Entwistle said.
"In 1993, it was designated in the Act, there is supposed to be a guides license."
Fish and Game weren't prepared to comment on the concerns, but say they're in the process of putting forward a case for guides to be licensed.