PORT HURON, Mich. -- Canadian authorities stopped an invasion this weekend: 1,500 people on inflatable rafts and boats that drifted across the border from Michigan during high winds on the St. Clair River.

The individuals were participating in the Port Huron Float Down, an annual event on the river that divides Michigan from Ontario. But the winds turned it into an international incident on Sunday.

Police in Sarnia, Ont., say the event has no official organizer and poses "significant and unusual hazards" given the fast-moving current, large number of participants, lack of life jackets, and challenging weather conditions.

They say it took hours for a bus service to transport approximately 1,500 U.S. citizens back to Michigan.

Staff Sgt. Scott Clarke told the Times Herald the float down participants were "unprepared to be stranded anywhere."

"It was a bit of a nightmare, but we got through it," he said. "There were long waits and long lines. They were cold and wet, but they all made it home."

The event started at Port Huron's Lighthouse Beach and was supposed to end at Chrysler Beach in Marysville.

Sarnia city workers spent several hours Monday picking up beer cans, coolers, rafts -- even picnic tables -- that washed up on the Canadian shore, said spokeswoman Katarina Ovens.

"I guess they were on the rafts," she said of the picnic tables.