Three of the Montreal's four beaches had their water quality ratings drop slightly due to an increase in the amount of e. coli bacteria.
The ministry of the environment blames the increase in the bacteria - which is usually found in fecal matter - on seagulls.
Helene Proteau of Quebec's environment ministry says seagulls like the beach, especially when humans and their food turn up.
Their droppings are the likely cause behind the drop in water quality.
The quality of water hasn't been affected badly - but it has been downgraded from A, considered excellent, to B, considered good.
That's still far from dangerous.
The beaches affected are the two on Cap St-Jacques and the one on Ile Bizard.
The water at the artificial beach at Parc Jean Drapeau is considered excellent.
It usually takes beaches a short time to install measures that will discourage seagulls from congregating at public beaches.