Fishing next to a mussel farm is one of the oldest tricks in the book, and almost a guaranteed catch.
But recreational fishers are being warned to steer clear this summer.
Mussel harvesters say the practice has become dangerous, with fishers coming too close.
The Firth of Thames is home to one of the largest mussel farms in the country, where skippers frequently invade the 30-metre exclusion zone around the harvester.
Waikato Regional Council harbourmaster Richard Barnett encourages boaties to fish there, but says they need to follow a simple rule - stay away from the harvesters.
"Lifting lines could break without warning, and that boat would be gone," he told Newshub.
Steve Wells of North Island Mussels says fishers are often competing for fish, but they needn't worry about that.
"You can catch a fish anywhere in these areas - you don't have to be close to the boat."