Poachers are allegedly pilfering trout at a popular fishing spot in Ngongotahā, near Rotorua, and some locals are furious.
A fishing club there said the culprits were fishing outside legal hours, using illegal methods and exceeding limits.
NGO Trout Fishing Club is run by volunteer retirees, and teaches young people to fish and respect the waterways.
Simon Aston is the club founder and told RNZ's Checkpoint, although times were rough, there was no excuse for the dodgy behaviour.
"We'd like people to keep to the practices of fishing games regulations and everyone will have a good time."
Trout fishing in the area is open from 5am until midnight, but Aston said there had been a spike in fishing during the banned times.
"I get reports from truck drivers going past early mornings, seeing cars parked there at 2-3 in the morning."
Aston had also seen other strange behaviour from the culprits, who he said often left their catches in peculiar spots.
"Someone might have been close to being caught, they'll hang their fish in the trees or under the flax bushes, and disappear through the creek and up the other side... and they'll come back later on and pick them up."
Aston believed the illegal catching may have something to do with spawning season.
"As spawning season comes, most of the fish in the lakes come to streams and they're in quite shallow water, so they are easy to catch."
Despite that, Aston said he wouldn't recommend keeping the catch.
"They're not good to eat at this time of the year... so you're better off to just leave them, and just catch and release."
Aston urged all people to respect the waterways, and stick to the rules and limits of trout fishing in the area, something he said the young people at the NGO Trout Fishing Club were happy to do.
"The youngsters that I deal with - and I have a lot of them - they just love it, because we supply the fishing gear and we supply a lot of fishing gear to people. Basically, $10,000 has gone out of my bank account this year, just buying fly-fishing gear for these unprivileged kids."
Regardless of the cost, Aston said he was happy to provide for the kids, given the atmosphere it brought to the place.
"There's kids laughing, screaming, they're just having a ball. The whole place is just thriving, especially in the early summer months."
All the fish find a home that's happy to have it.
"We give fish away also to Kōhanga Reo and that sort of thing, also to unprivileged people, people that can't fish," he said.
"We have quite a little community here, where we can put fish to anybody. You know, it's a small town, so it's easy to get around."
As for the best way to serve the fish, Aston recommends cold smoked trout, which tastes "just like salmon".