A powerful wave pulled a group of swimmers out to sea from a seawater pool on Spain's Tenerife island, killing four people and leaving one missing, according to Spanish authorities.

The incident unfolded at Isla Cangrejo on the Los Gigantes coast, a popular spot for foreign vacationers on the island's rocky western shoreline. Crews used jet skis and helicopters in the rescue effort. Three bodies were recovered on Sunday, and a fourth victim, a woman who had been revived at the scene and airlifted to a hospital, died on Monday.

Spanish authorities did not release the names of the dead, but AP reported that the bodies recovered on Sunday included a 35-year-old man, a 55-year-old woman and another man whose identity was not given. No additional details were provided about the missing swimmer. Rescue crews were still searching on Monday.

Local media reported that a weather advisory for rough seas was in place when the swimmers were swept away. One report said the pool had been closed to swimmers since Dec. 3. Residents quoted by local media said the danger was well known and that signs and fencing had been put up to keep people away during unsafe conditions. They said anyone who is dragged from the pool onto the slippery rocks below has little chance of getting back up once they lose their footing.

The pool sits at nearly sea level and is bordered by volcanic rock on one side and a cement barrier on the other. That design makes it inviting in calm weather but dangerous when heavy surf overtops the barrier. Emilio Navarro, the mayor of Santiago del Teide, offered condolences to the families of the dead and said authorities regularly warn bathers not to use the pool when the sea is rough.

The deadly wave came after a similar pattern of danger elsewhere on Tenerife. In November, strong waves killed three people and injured 15 on the island during a tidal surge. The latest deaths are a reminder that even places marketed as scenic swimming spots can become lethal in minutes when weather conditions change and people ignore closures or warning signs.

The pool's design helps explain why the deaths were so difficult to prevent once the wave hit. Bordered by volcanic rock on one side and a cement barrier on the other, Isla Cangrejo sits almost at sea level, which makes it attractive in calm conditions but vulnerable when surf overtops the barrier and throws people onto slippery stone. Residents said that once swimmers are pushed beyond the barrier, the rocks below make it hard to climb back.

That local warning system was central to the account from authorities and residents alike. Local media said signs and fencing had already been put in place and that the pool had been closed for days because of rough seas, yet people still entered. The result, according to the AP account, was a rescue operation that relied on jet skis, helicopters and repeated search efforts, with one swimmer still missing after the initial recoveries.