When rescue arrived the boat was fully engulfed but all occupants had already been safely transferred to a second watercraft and taken to shore.
Sheriff's Marine Division transported fire department personnel to the scene who then extinguished the fire.
The 19 foot Seadoo watercraft had blown to shore of an unnamed island west of the boat launch.
The owner Ryan Hammack, 28, of Marquette said he and three passengers had just launched the boat when he noticed smoke coming from the instrument panel and engine compartment. A fire extinguisher was used with no success. A passerby in another boat was flagged down and a second fire extinguisher was used with no results. All parties in Hammack's boat were evacuated by the passerby and taken to shore.
No one was injured at the scene.
Arrangements are being made to remove the remainder of the boat by the owner.