The same weekend a layers-wearing mob of thousands descended to the banks of the Charles for the annual Regatta, one man stripped down and took a naked plunge into Boston’s icy offshore waters, according to State Police.

The unusual encounter Saturday afternoon began when bystander alerted a state trooper about a nude man standing near the Steriti Memorial Rink on Commercial Street at about 1 p.m., police said.

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The man took off through a nearby baseball field, jumped a fence and dove into the chilly Boston Harbor, the police report said.

Troopers from the State Police Marine Unit fished the man out of the harbor and administered first aid for possible hypothermia, police said. He was taken to an area hospital for treatment, according to the report.