The fire was first reported at 2:44 p.m. near state Highway 29 and Perini Road south of the lake, Cal Fire officials said.
The 300 acres burning have been 20 percent contained. Forward spread of the fire has been stopped. Mandatory evacuations were in effect for the Mercy Spring area.
Voluntary evacuations were also in effect for the Twin Lakes area as well.
Highway 29 remains closed in the area of the fire.