Alright, so it was an unintentional invasion, but an invasion nonetheless.
Strong winds during the annual Port Huron Float Down pushed about 1500 people from the U.S. side of the St. Clair river over the border and onto the shores of Sarnia. All participants were floating on dinghies, inner tubes, and rafts, and arrived without passports or IDs. This caused some major problems for law enforcement on both sides of the border.
With the help of police, border security, and coast guard agencies, the stranded Americans were rounded up and sent back to Port Huron, Michigan.
Each August, participants in the Port Huron Float Down assemble at Lighthouse Park, where Lake Huron feeds into the St. Clair River. People launch themselves from the bank in the morning and ride the current south about 14 kilometres down to Marysville, Michigan. This year saw the largest number of people ever floating that far off-course. In 2011, about 100 boaters ended up in Ontario when a nasty storm went by that spawned a tornado in Goderich.
It’s a wonder this doesn’t happen more often, as less than a kilometre separates the US and Canada along the St. Clair River.