It happened about 3:30 Thursday afternoon near Clark Street.
A passenger saw the man fall off a bridge. The boat's captain says he believes he was in the water for 10 to 15 minutes before they could get to him.
"My deckhand was able to get down with a passenger's help and was able to get down and retrieve this person and pull him up on the deck and start checking his vitals and started doing compressions and rescue breathing," said Capt. Eric Gierzynski, Shoreline Sightseeing.
Police say the man is in his forties and was wearing a bike helmet and backpack.
His name hasn't been released.