Freedom campers and migrant workers are increasingly fishing without permission throughout the South Island.

Increasing numbers of freedom campers are fishing illegally in lakes and rivers, with some fleeing the country before they can be prosecuted.

Fish & Game officers are pursuing wrongdoers "to the ends of the Earth" to pay their debts, but say they are struggling to deal with an increase in illegal fishing.

Officers are reporting larger numbers of overseas visitors fishing without licences, amid the tourism boom in parts of the South Island.

SUPPLIED Overseas visitor the Queen Mother fishing at Lake Wanaka in 1966. Her visit predated the current licensing system, so she was not breaking the law.

Some flee the country before paying the $500 fine, risking potential court action if they return.

It is an emerging problem in tourism hotspots such as Queenstown and Wanaka, where backpackers have taken to "opportunistic" fishing in picturesque freshwater lakes.

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Overseas visitors, particularly freedom campers, have been accused of defiling parks and scrapping with locals in recent weeks.

"They are upsetting quite a lot of the local anglers," said Fish & Game North Canterbury general manager Rodd Cullinane.

"We are under quite a lot of pressure to try and sort it out, if you like."

This week a French visitor was spotted trout fishing in the polluted Avon River in central Christchurch, next to the quake-damaged Bridge of Remembrance.

He left the country before he could be prosecuted.

In North Canterbury, immigrant workers working on farms and the rebuild were often found fishing for kahawai along the Waimakariri River without licences, Cullinane said.

"In a general sense, we're processing a lot of prosecutions . . . although there's little we can do, other than take an educational front. We don't like prosecuting every person."

All non-residents are required to have a licence to fish in New Zealand.

A one-day licence costs $20, and a full-season licence costs $161.

The system was introduced after high visitor numbers began putting pressure on fisheries.

Near the tourist traps of Wanaka and Queenstown, there has been a sharp uptake in illegal fishing among tourists, many of them backpackers.

The perpetrators were often freedom camping, and in some cases, had found their fishing rods in the vehicles they had bought from other freedom campers.

"We've got a bit of an epicentre for it," said Fish & Game Otago operations manager Ian Hadland.

"We've got those very touristy areas like Wanaka and Queenstown and Cromwell, and there are a lot of foreign people and transients there."

The number had increased noticeably this year, he said, coinciding with the tourism boom in the region.

There were nine prosecutions under way already, including visitors from Germany and Australia.

Some opted to pay the $500 on the spot fine to avoid a court appearance, but others fled the country.

New Zealand's fishery resources were not limitless, and the interests of Kiwis had to be protected as well, Hadland said.

"We welcome foreign tourists to fish our waters, but at the same time we must enforce the rules to protect our fisheries and some of the best angling worldwide."

While the local council had trouble receiving fines from law-breakers – about half do not pay their fines – Fish & Game had been more successful.

"We're getting as many details as we can and almost pursuing them to the ends of the earth, to the point where they're actually sending money back from overseas to clear up their offending.

"While we don't have a great deal of clout, if you follow these people and are persistent, you can generally get a result."