With the London region, including Sarnia-Lambton, under a severe thunderstorm watch, The Canadian Coast Guard is advising people not to participate in the annual Port Huron Float Down Sunday.

"(It) poses a risk due to water temperature, weather conditions, fast current and a large number of participants, the Coast Guard says in a Tweet. "Please stay safe and do not participate."

Environment Canada says conditions are favourable for the development of dangerous thunderstorms Sunday afternoon and evening.

London-Middlesex, Sarnia-Lambton, Elgin and Huron-Perth are all under the advisory.

The agency says strong wind gusts can damage buildings, down trees and blow large vehicles off the road.

It says severe thunderstorms can produce tornadoes. Heavy downpours can cause flash floods and water pooling on roads.

The Float Down is popular with people on both sides of the border. On the event Facebook Page, organizers are also advising people not to enter the water.