In the women's race over the same distance, Ana Marcela Cunha of Brazil won her second gold of the championships, finishing in 5 hours, 8 minutes 03.00 seconds, 8.60 seconds ahead of second-place finisher Finnia Wunram of Germany. Lara Grangeon of France claimed the bronze, 18.20 seconds behind Cunha.
It was the 27-year-old Cunha's fifth gold and 11th medal overall at the world championships since 2011. She won the 5-kilometer race here on Wednesday.
Reymond finished the men's race in a time of 4:51.6.20 while Belyaev clocked 4:51.06.50. Alessio Occhipinti of Italy earned the bronze medal, 3.30 seconds behind Reymond in often heavy rain.
Another Italian, Simon Ruffini, was fourth, 8.70 seconds behind. Australian Kai Edwards took fifth, 11 seconds behind Reymond.
The top Americans in the men's race were David Heron in 14th place, 4 minutes, 05.60 seconds behind the winner, and Brennan Gravley, who finished right behind Heron in 15th, 6:11.30 behind.
American Erica Sullivan was fifth in the women's race, 3 minutes, 20.20 seconds behind Cunha, while teammate Katy Campbell finished in ninth place, 3:56.60 behind the winner.
Only two of the 24 starters failed the complete the men's race, while five of 21 women did not finish their race.
The 25-kilometer races ended the seven-event open water program at the worlds. Only two open-water events will be held at the Tokyo Olympics next year — the men's and women's 10-kilometer races — and the top 10 finishes here qualified for those events.