A man was found dead in the water during a swimming event on Thursday at the CrossFit Games, an international competition being held in Fort Worth that draws some of the world’s fittest competitors.

The man had been swimming in Marine Creek Lake, the authorities said. Search-and-rescue crews were called on Thursday morning after the athlete had not been seen for some time.

The Tarrant County Medical Examiner’s Office identified the man as Lazar Dukic, 28, of Serbia. The cause and manner of Mr. Dukic’s death had not yet been determined.

The competition attracts hundreds of thousands of competitors who participate in CrossFit, a high-intensity fitness program that incorporates strength training and aerobics workouts. The competition started in February, as the fields narrowed down to the quarterfinals in April and the semifinals in May. The final round of the CrossFit Games were scheduled to conclude this weekend in Fort Worth.

Don Faul, the chief executive of CrossFit, the company behind the games, said during a news conference on Thursday that “CrossFit is deeply saddened by the death of one of our athletes.”

The finals, taking place from Thursday through Sunday, were being streamed online. In videos of Thursday’s event that were circulating on social media, Mr. Dukic appeared to be struggling to swim toward the finish line.