The group representing South Island commercial eel fishermen is investigating the fishing of tame, 80-year-old eels from Lake Moeraki, in South Westland.
Even though the lake is a scenic reserve and within a World Heritage site, the fishing was allowed under the current law.
Eco-tourism operator Gerry McSweeney, who operates the Lake Moeraki Wilderness Lodge at the outlet to the lake, said it should be illegal to take eels from a protected area.
South Island Eel Industry Association spokesman Bill Chisholm said this week they were investigating.
Mr Chisholm said it did not appear any rules had been broken, but he was looking into whether the industry's own code of practice had been breached.