U.S. Border Patrol agents arrested the 24-year-old man near Marine City, Mich., after a resident tipped off the local law enforcement dispatch office to the unusual swimming regimen, WXYZ-TV, Detroit, reported.
The scuba diver, whose name wasn't released, was spotted on surveillance cameras pulling what appeared to be a so-called dry bag used by divers, the TV station said. When they took the man into custody, they allegedly found the stash of pot secured in a watertight PVC cylinder tied a seawall ladder in the bag.
"We picked up his image on our camera and could see he was carrying something," U.S. Customs and Border Protection spokesman Kris Grogan told The Macomb Daily in Mount Clemens.
The suspect was turned over to St. Clair County authorities.
Grogan said it was the first time he'd ever heard of the drug-smuggling strategy.
"It's not something you see every day, but there's always something going on around here, that's for sure," he said.