Families feeding the ducks and geese in Ely in Cambridgeshire could face fines of up to £2,500.
The city's wildfowl population, which includes Muscovy ducks, have long been a tourist attraction but they have also attracted numerous complaints from residents about bird mess on the pavements by the river.
Now East Cambridgeshire District Council has put up a sign warning people to feed the birds on the water, not on the ground - or face a fine.
Councillor Richard Todd said the fines would only be imposed if persistent offenders ended up in court.
"We've got an enormous amount of complaints from residents about how much of a messy area this is. Ely in general is an extremely clean place and the river is so much of an asset. "We would try and educate people and talk to them about what they are doing. What we want to do is sharpen people's minds and if we discovered anybody was feeding we'd talk to them and explain to them. A fine is a last resort."
Some holidaymakers in Ely today branded the fine "extortionate".
Linda Barnes said: "I think it's important that people get close to nature and see it in all its different forms - even the mess.
"Even if people didn't feed them they'd still be messing in the grass. They just like to congregate here."
It's not the first time the council has come under fire for its policy on wildfowl in Ely. A scheme to oil eggs to stop new chicks from hatching was very controversial.