Russian free diver Natalia Molchanova remains missing three days after she went on a recreational dive off Spain's Balearic Islands and never resurfaced.
Molchanova, 53, is considered by many to be the greatest female free diver of all time.
The international free-diving federation AIDA and Molchanova's family said she went on a 30- to 40-meter free dive off the coast of Formentera Island in the Mediterranean Sea on August 2 but did not resurface.
Molchanova, a mother of two, is the most decorated free diver in the world, with 41 world records and 23 world championship titles.
Free diving is a form of underwater diving in which divers hold their breath instead of using breathing apparatus such as a scuba tank.
Molchanova's feats include holding her breath for more than nine minutes and diving to a depth of 101 meters using a fin.