It happened at about 12:40 p.m. near Jones Brothers Park, said the Travis County Sheriff’s Office.
That's on the northern side of the lake in Jonestown.
911 callers said that no one was on the boat, which was docked when the flames broke out, TCSO said.
It took crews about 30 minutes to knock the fire down.
There were no reports of any injuries or what caused the fire.