After a lengthy search of the waters off the Balearic Islands, free-diving champion Natalia Molchanova has been presumed dead.

Spain’s maritime rescue service and the police underwater team have called off the search for the diver, switching now to scanning the surface of the Mediterranean Sea off the coast of the island of Formentera (near Ibiza) for any sign of the 53-year-old Russian champion, who disappeared during a dive Sunday. A submersible robotic device hired by her family will continue to search below the surface while authorities keep watch on the surface.

Her son, Alexy Molchanov, said his mother was not expected to be found alive, a conclusion shared by the community of free divers. “It seems she’ll stay in the sea,” he said (via the New York Times), making peace with the possibility he may never have closure. “I think she would like that.”

Molchanova, who was diving without fins, was using small weights during the dive to a depth of 100-130 feet. The search was “very complicated,” rescue coordinator Miguel Felix Chicon said because of tricky currents and water temperatures that can drop quickly below the surface and shock a diver.

Molchanova, who has set 41 world records in the sport, was diving merely for fun with three others, her son told the New York Times. She was not tethered to a safety line and, Chicon told the Guardian, if she took off the weights, the currents could have carried her far.

“She was a free-diving superstar, and we all thought nothing could harm her,” Kimmo Lahtinen, the president of the global federation for free diving (AIDA) told the Times. “Nothing could happen to her, but, you know, we are playing with the ocean, and when you play with the ocean, you know who is the strongest one.”

In constant weight free diving (one of three depth disciplines) , a diver uses a monofin and swims as deeply as possible on one breath. Any weight worn on the way down must be brought back to the surface. For Molchanova, diving was a mystical experience and training in a pool wasn’t the same as jumping into the ocean.

“Free diving is not only sport, it’s a way to understand who we are,” she told the New York Times in 2014. “When we go down, if we don’t think, we understand we are whole. We are one with world. When we think, we are separate. On surface, it is natural to think and we have many information inside. We need to reset sometimes. Free diving helps do that.”