The girl was on the back end of the boat around noon as it slowly approached a dock at Markley Cove at the south end of the lake, Capt. Tracey Stuart said.
The exhaust began to affect the girl, who was wearing a flotation device, and she fell into the water, Stuart said.
The girl's father saw her fall and rescued her, Stuart said.
The close call comes on the heels of a drowning and a near-drowning over the weekend.
On Sunday afternoon, Kevin Yip, 24, of San Francisco, drowned in the Pleasure Cove area of the lake when he jumped off a pontoon boat to swim without a flotation device.
He was seen struggling in the water before he disappeared. Sheriff's divers recovered his body Monday morning.
The same afternoon that Yip drowned, a 6-month old baby became trapped under a capsized boat on the lake. The child was taken to a hospital but is expected to survive, Stuart said.