An investigation is under way into moves to open up a Norfolk pike fishery for jet skiing.
Jet skiers have been using a nature reserve at Pentney Lakes, near King's Lynn.
Planning agreements in place at the beauty spot state Bird Lake should be kept as a nature reserve and used only for windsurfing and fishing.
Jet skiers were supposed to be confined to a smaller, neighbouring lake on the complex.
But a channel has been dug connecting it to Bird Lake and estate agents are advertising jet skiing as being available for people buying chalets at Pentney.
Anglers are allowed on limited areas on Bird Lake outside the breeding season for rare species like terns.
The restriction means the lake is only accessible during the winter months, when its only visitors tend to be pike anglers.
"Those of us who fish the place are happy to co-operate with the restrictions because we recognise we have to co-exist with the wildlife," one said.
"But if we go along with the rules and only fish when are where we're supposed to, it seems unfair if jet skiers can use the lake when birds are fledging.
"There's also the question of what damage they could potentially do with their wake and disturbance, which is why water skiing was not permitted on Bird Lake in the first place, and why the only water borne activities permitted are angling and wind surfing."
A planning agreement drawn up between the lakes' owners, the council and conservation group the Norfolk Wildlife Trust, divides the site into a number of zones.
They include a "buffer zone" where there should be "reduced levels of activity". But two-storey holiday homes have been built close to the zone, which includes an area frequented by otters.
Now the owners of one property have applied for planning permission to live in it all-year-round, while a hot tub and decking have been built alongside one of the lakes.
Pentney Lakes declined to comment. The council said an investigation was under way, with a view to a "more robust" management plan being drawn up.
It added: "These recommendations may or may not include formal enforcement action."
Ward councillor Janet Murphy said: "The intention is to get a more robust management plan to make sure that the wildlife is protected. We need to protect our countryside."