People in Hove are being asked to stop feeding a group of swans which has taken up residence on a boating lake.
Hove Lagoon needs to be cleared of debris to prevent disease
There are concerns for 30 birds which have made Hove Lagoon their home.
Brighton council says it needs to drain the 3ft pool, used for windsurfing lessons in the spring, to clear debris such as trolleys, bottles and cans.
East Sussex Wildlife Rescue Service (Wras) said swans fly off when water levels drop but feeding tempts them to stay and they could be left stranded.
Trevor Weeks, from Wras, said: "These birds should really be living in a more natural habitat.
"But their numbers have grown because of artificial feeding by residents.
"If feeding continues they would stay indefinitely but if it stops they should quickly realise and move on.
Mr Weeks' colleague Maz Smith said: "I have seen a swan badly cut in the lagoon, probably by debris, so the situation cannot be left as it is."
Chris Holm, council resort services manager, said: "The lagoon is used for teaching families and children to windsurf from around Easter.
"It is vital for safety reasons the pool is drained and cleared of things like shopping trolleys, bottles and cans.
"Otherwise we could not go on using it and it would become dangerous for the birds themselves."