Firefighters were called shortly after 11 p.m. to 2040 Westlake Ave. North to a fire that appeared to be located right next to the dock.
Crews say the fire involved two houseboats and two docked boats. All residents were evacuated.
Seattle Fire says the fire was particularly challenging because of limited walkways and weight limits on the floating docks.
Rescue swimmers were on scene in case anyone fell into the water and Harbor Patrol assisted with pouring water on the fire from the lake.
No injuries were reported and the cause of the fire is under investigation.