Fly fishing is one of the last amateur sports, and anglers compete purely for the glory of catching big fish.
"There's no prize money," says Jill Mandeno, international organiser of the World Fly Fishing Championships.
"All they get is a medal, maybe a gift."
A total of 128 competitors from 23 countries have descended on Rotorua for the nine-day event, which runs until next Sunday.
Over the next week, they will fan out across five rivers and lakes in the region in their quest to catch a prize-winning trout.
But the anglers do not keep their catches - contest rules require them to release any fish caught back into the waterways alive.
They must use barbless hooks and knot-less nets to lessen the chance of injuring the trout, and if for some reason one does not survive, it is not weighed or measured.
"Dead fish don't count," said Ms Mandeno, who is also president of Sport Fly Fishing New Zealand.
She said fly fishing in New Zealand was a unique experience for most of the overseas competitors because it was probably the first time they had fished for "wild fish".
New Zealand differs from many other fly-fishing destinations in that only tiny "fingerling" fish are released into rivers.
In Europe, fish are bred in hatcheries and not released until they weigh up to 700g.
Such stock fish behaved differently to wild fish, Ms Mandeno said, and New Zealand's wild fish were also much bigger - up to 3.5kg.
Local fish stocks were also more plentiful than in other countries, and 80 to 90 per cent of competitors were likely to catch fish in every session, whereas at a competition in Portugal, less than a quarter of anglers caught anything at all.
A European angler had told Ms Mandeno that New Zealand fly fishing was the best he had ever experienced.
"They're just so excited," she said.
She said the lack of prize money did not stop anglers being competitive.
Winning the world title could enable an angler to command a high price as a guide.
Most competitors were in their mid- to late twenties, and had to be fit to stand up to the rigours of hours of casting and standing in sometimes ice-cold water. Because of this, competitive fly fishing tended to be a male-dominated sport.
Only two women had entered, both from Japan, but a New Zealand woman planned to compete in the Commonwealth championships, being held in Hastings the week after the world event.
The only thing taking the sheen off this week's competition was the threat of the "rock snot" alga didymo, which has infected South Island waterways.
Felt-sole boots and waders have been banned at the world championships in an effort to stop its spread, and cleaning stations for gear have been placed at all the fishing spots and the competitors' hotel base.
The competition is in its 28th year and was last held in Rotorua in 1991. It is expected to put up to $3 million into the local economy.