According to Hudson Fire Chief Scott St. Martin, no one was injured when the boat exploded.
It drifted back into the water but has since been removed from the river.
The chief said Hudson fire had to wait for Stillwater, Minnesota, to assist, because his department does not have a fire boat.
Police say the owner was trying to get it on a trailer at the boat launch when the explosion happened.
The boat was engulfed in flames, and debris landed near the shoreline.
Park visitors were evacuated before the fire was extinguished.