Natalia Molchanova set a world record for dynamic free diving in September 2014 (video below), but she is believed to have died off the coast of Spain while free diving for fun with three friends on Aug. 2.
Molchanova, who held 23 world championship titles and 41 world records, was diving in the Balearic Sea when she disappeared, notes CNN.
The 53-year-old Russian could reportedly hold her breath for up to nine minutes, but never surfaced. Molchanova was wearing weights of around 1 to 2 pounds to help her dive.
Her fellow divers searched for her, and then radioed for help, which included private boats, the local coast guard and a helicopter, reports The New York Times.
The search resumed on Aug. 3, and added an underwater robot the next day, but Molchanova wasn't found.
Her family and AIDA International, which governs free diving, said in a statement on Aug. 4:
"Natalia Molchanova was recreationally freediving off the coast of Spain on August 2, 2015 when she was separated from her peers. She was diving without fins to around 30 to 40 meters (98 to 132 feet) and (supposedly) got into (a) strong underwater current.
"Search efforts have been ongoing during daylight hours and the next day since she was reported missing by three peers. She disappeared while diving approximately two miles (3.2 km) northwest of the port of La Savina at Poniente de es Freus."
Molchanova's 28-year-old son Alexey Molchanov told The New York Times: "It seems she'll stay in the sea. I think she would like that."