A 15% increase in mooring fees could be the end of the hobby for many small boaters in the island, according to the Guernsey Boatowners' Association.
The proposed rise forms part of the Public Services Department's latest plans for raising an additional £1m from the island's harbours and airport.
President Peter Derham said the increase was simply too much for many boat owners to bear.
He said the rise would be "disastrous" for the majority of boat owners.
Mr Derham said: "A lot are just going to give up, they're not going to be able to afford to run their boats."