The Lake Taupo District mayor is worried that if a local iwi charges Ironman New Zealand to use the lake for their triathlon event other event organisers could be put off and local businesses could lose money.
Ngati Tuwharetoa legally owns the lake, but not the water.
Ironman New Zealand is to host the annual swim, cycle and run competition in Taupo in March.
Mayor Rick Cooper says even though the tribe does have the right to charge users for the lake, it could have devastating effects on the district's economy.
He says local businesses depend on big events like this to generate money for the district.
Mr Cooper says the proposed levy by Ngati Tuwharetoa could jeopardise future events and if the central North Island town loses the lucrative Ironman event he would be very, very upset.
Ngati Tuwharetoa is refusing to comment, saying it is unable to talk about ongoing commercial discussions.
Te Manu Korihihas been told Ironman New Zealand and the iwi are expected to hold talks and that the tribe is not considering charging individual Ironman competitors, but instead charging event organisers.