Four people died and one remained missing after a powerful wave dragged a group of swimmers out to sea while they were in a popular seawater pool along the rocky, western coastline of the Spanish island of Tenerife, Spanish authorities said Monday.

Crews recovered three bodies on Sunday, a 35-year-old man, a 55-year-old woman and another man about whom no information was given, during a major rescue operation that used jet skis and helicopters to locate and pick up all those dragged out to sea.

The fourth, a woman, died Monday, a day after being revived at the scene and airlifted to a hospital.

No additional information about the identities of the victims was provided.

The pool at Isla Cangrejo, on Tenerife’s Los Gigantes coast, is popular with foreign tourists, according to local media.

Bordered by volcanic rock on one side and cemented off from the sea on the other, the pool sits at nearly sea level and can be dangerous during rough seas when large waves can easily overcome the cement barrier.

Local media reported that a weather advisory for rough seas was in effect at the time when the swimmers were swept out to sea. One media outlet reported that the pool had been closed to swimmers since 3 December.

Area residents said swimmers had ignored signs and fencing put up to prevent anyone from going into the pool because of the weather conditions. They said it’s very difficult for anyone dragged out to sea to get a foothold on slippery rocks just below the pool.

“People…don’t know how the sea is here, and the danger of the pool, because there are rocks below on which people fall and can’t get back up. It’s very dangerous,” said one local resident.

Emilio Navarro, the mayor of Santiago Del Tiede, offered his condolences to the families of the dead and said rescue crews continued on Monday to search for the missing swimmer.

He said authorities take steps to warn bathers of the dangers and to dissuade them from using the pool during rough seas.

“We…ask people to pay attention to the signage put up by the authorities,” he said. “It’s to take care of and protect everyone.”