It so clean the Coast Guard has to stop people from swimming across the harbor's shipping lanes. The Coast Guard reports:
A local citizen notified Coat Guard Sector Boston that the man had jumped into the water from [Rowes Wharf] at about 9:15 a.m., and was swimming north, across the ferry channel, toward the John Joseph Moakley Courthouse.
Two Coast Guard vessels responded and pulled the unidentified man out of the water. Click the photo below for some video of swimboy: