Anglers appear to be avoiding Lake Rotoiti because of the lake's poor water quality.
Fish and Game regional manager Steve Smith said anglers were clearly avoiding the lake, and licence sales were falling significantly as a result.
Purchase of short-term and 24-hour licences had dropped more than 20 per cent from lastyear, he said. Before the public was aware of the lake's poor water quality, more than 45,000 anglers visited Lake Rotoiti each year.
"The irony is that people are not visiting the lake despite the fact that it has been fishing well. While the fish are not as large as they once were, they still average 1.7kg and the catch rate has been excellent."
Mr Smith said it was not only anglers likely to be affected by Lake Rotoiti's problems.
Research indicated trout fishing on Rotorua's lakes contributed $30 million to the community, he said.
"Unless a solution is found quickly, the same result is likely to spread across other lakes. People from other areas tend to view the Rotorua lakes as a single entity and as a result see all the lakes being affected.
"We simply cannot afford to leave the lake the way that it is at the moment."
