SHERMAN ISLAND, Calif. -- Contra Costa County officials have cancelled a health advisory after smoke produced by a fire on Sherman Island spread dangerous particulates across Bay Area skies.

The fire sent vast plumes of smoke across Bay Area skies Friday night and had burned out by Saturday morning. Large swaths of the barren island have been charred black.

Because of its inaccessibility, firefighters on Friday decided to let the blaze burn itself out.

The island is just a short distance across the water from Antioch, Pittsburg and Baypoint. The smoke could be seen from miles away.

This fire broke out around 11:30 a.m. on a small island at the southern tip of Sherman Island. Crews are allowing the fire to burn itself out because there is no road access and the water is too shallow to bring in fireboats.

The island is uninhabited. There are no buildings; just vegetation.

Perhaps of a bigger concern were the huge plumes of smoke and ash produced by the fire raining down on the nearby communities of Pittsburg, Antioch, Baypoint And Concord. Contra Costa County officials issued a health advisory friday afternoon.

They asked people with respiratory problems to stay indoors. One ten-year-old girl told us her school kept students inside beyond dismissal time Friday.

"Afterschool, they told us to stay inside because of the ashes raining around the school. You can't breathe it from so much smoke," said Kierra McCoy of Pittsburg.

At a strip mall near Highway 4 in Pittsburg, vehicles were covered with ashes.

"When I came out of the mall I thought it was raining. I came out and realized it was a fire. I was on the freeway and had the sunroof open and the stuff was coming into the car," said Leah West of Pittsburg. "It's amazing."

West was understandably anxious to get inside with her 16-month-old daughter.

"We both have upper respiratory infections. We're getting over colds," explained the concerned mother.

Other people also downwind from the fire told KTVU the smoke and ashes affected them as well.

Fire officials say they don't know how the fire started, but Sacramento Regional Fire said they received a report of two people leaving the island on a boat.