SAN FRANCISCO, California — One person died, three people were missing and 16 were rescued from the waters off San Francisco after a pontoon boat sank Tuesday afternoon while carrying mostly family members as part of a memorial service, authorities said.

Crews arriving on the scene near Alcatraz Island found a three-deck pontoon vessel almost fully under water with the motor still running and leaking fuel, San Francisco Fire Chief Dean Crispen said.

One dog aboard the vessel also died.

“The reports we’ve had from witnesses was that there were rough seas and the vessel began to take on water and was turned over in the bay,” said Crispen.

Officials say they’re still piecing together exactly what caused the three-story, 50-foot pontoon boat to sink.

Crispen said the vessel was believed to have launched near the St. Francis Yacht Club in San Francisco. A person who answered the phone there said the club did not have any information on what happened.

Longtime San Francisco Bay sailor Mike Peterson tells me incidents like these are rare.

“It would take something happening very rapidly to cause a boat like that to go down and people like that to end up in the water,” said Peterson.

The U.S. Coast Guard says they are still conducing searches for the three missing people as a rescue rather than a recovery mission.

Despite that, Peterson says the possibility of being out in the water for that long has multiple challenges.

“You have the wind coming one way and the tide coming another. It makes it very choppy and rough. Especially in the afternoons. That’s exactly what happened here,” said Peterson.

Whatever the odds may be though, officials say they’ll be searching all night.

“We have modeling software that predicts the location of where our missing mariners could be. We use that very strictly in where to provide assets. And throughout the night we will have surface and air assets providing coverage.”

The Associated Press contributed to this report.

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