A cabin cruiser carrying 20 adults on a memorial outing capsized in rough seas approximately 600 yards off Alcatraz Island Tuesday afternoon, killing one man and leaving three people missing as U.S. Coast Guard crews searched through the night.

The Volare, a Stockton-based three-story vessel, overturned in San Francisco Bay at around 3:37 p.m. Tuesday after taking on water in challenging conditions. One man died despite CPR; sixteen people were rescued — some by private boaters who arrived ahead of official crews — and three were hospitalized in stable condition. The cause has not been officially determined, and the investigation is ongoing.

The Volare — described by San Francisco Fire Department Lt. Mariano Elias as roughly 50 feet in length and three stories tall — had departed the St. Francis Yacht Club before taking on water and overturning, according to KQED. Sixteen people were pulled from the cold, choppy water; three were transported to local hospitals and are in stable condition. A dog aboard the vessel also died.

Fire Chief Dean Crispen told KQED the cause of the capsizing remained under investigation. "The reports we've had from witnesses is that there were rough seas, and apparently the vessel began to take on water and was turned over in the bay," Crispen said.

Witnesses aboard a nearby recreational vessel who reached the scene before emergency crews described a chaotic scramble. "There were people clinging to the top of it, there were people in the water, a lot of debris scattered all over the place," a crew member who asked not to be identified told KTVU. "Four or five people were hanging onto the top of that boat, and they were waiting to be taken out of that water." She also relayed a grim detail reported to her by other early responders: "They said that there were two people that were banging on a window and trying to get out."

Before official rescue vessels arrived, a captain of a nearby boat tossed life jackets to those struggling to stay afloat and rescued a woman with a head injury who had been clinging to a floating board, KTVU reported. The anonymous crew member described the survivors as appearing "middle-aged to elderly" and visibly struggling against the current.

Officers with the San Francisco Police Department's Marine Unit were the first official responders on scene. Crispen told KQED they found a man in the water in severe distress, pulled him aboard, and initiated CPR — but he was pronounced dead upon arrival at Gas House Cove in the Marina District. His identity has not been released. Crispen described the overall first responder effort as "nothing short of heroic," according to the San Francisco Chronicle.

The U.S. Coast Guard assumed lead authority over the search for the three still-missing passengers, deploying both surface and air assets and relying on predictive modeling to track likely drift patterns. "We have modeling software that predicts the location of where our missing mariners could be," Coast Guard Lt. John Corvino told KQED. "We use that very strictly to provide assets, and throughout the night we will have surface and air assets providing coverage."

Crispen said the 20 passengers were mostly family members or people who knew one another, gathered for what he believed was "some kind of memorial service" when a wave struck and the boat capsized, the San Francisco Chronicle reported. The investigation into the cause of the capsizing remains ongoing.