ISTANBUL — Turkish coast guard and maritime police vessels in Istanbul were searching Monday for a Russian swimmer who went missing during a cross-Bosphorus race a day earlier, state-run media reported.

The swimmer, named by the Anadolu news agency as Nikolai Svechnikov, failed to complete the 6.5-kilometer (4-mile) annual race from Istanbul’s Asian shore to the European side.

More than 2,800 swimmers from 81 countries took part in Sunday’s competition, considered one of the world’s leading open-water races.

Swimmers face strong currents and choppy waves while traversing the waterway, which links the Black Sea to the Sea of Marmara and divides Turkey’s largest city. The strait was closed to maritime traffic for the event, which is organized by the Turkish National Olympic Committee.

SwimTrek, a company offering entry to the race, describes race conditions as “challenging” on its website, adding that “experience of swimming in all sea conditions is essential.”

In a statement, the Olympic committee said it was “deeply saddened by the disappearance of one of our athletes during the race.”

It said 100 vessels, including boats from various emergency services, were monitoring swimmers during the race. At the end, the route was scanned for stray competitors and none were found.

Officials realized a swimmer was missing by comparing the lists of participants and those who finished, the statement said.