Authorities in Magog, Que., are trying to identify a Memphrémagog Lake snail believed to be hosting a nuisance parasite that is causing swimmers to break out in a rash.

The schistosome parasite most often latches on to snails and ducks to survive, but will sometimes burrow into human skin.

The parasites don't survive long after choosing a human host but they leave a trace.

The result is an irritating rash called swimmers' itch, said Sophie Paré, a biologist and co-ordinator of the Memphrémagog Lake patrol.

"It's not severe, but the itching can last up to 10 days," although it does not cause any long-term health problems, she said.

Several swimmers in the popular lake have complained about the itch, Paré said.

The city of Magog is trying to identify the type of snail hosting the parasite so that divers can remove them from swimming areas.

Until then, people should slather themselves with sunscreen to ward off the pests before swimming in the lake, Paré said.

A vigorous shower after swimming in the lake also helps minimize any rash.