Fire started on one boat docked near the edge of Harbor Island and then spread to another late Thursday.
The call came in to San Diego firefighters just before 10 p.m. with a report of an explosion at the marina located near 2040 Harbor Island Drive.
Crews found a boat on fire and began battling the flames until the fire was out the boat had sunk.
Unfortunately, flames caused damage to a second boat.
Harbor police divers searched the area surrounding the boat for anyone who may have fallen overboard.
No one was injured.
The cause of the fire was unknown.