One person has died and three are missing after a three-deck pontoon boat sank near Alcatraz Island in San Francisco on Tuesday afternoon. 16 people were rescued and authorities said the boat was carrying mostly family members who had gathered for a memorial service. The vessel was found almost completely submerged. Divers, helicopters and rescue boats are continuing to search for three people who remain missing. #BoatSinking #Alcatraz #Channel4News #C4News