Valerio Cleri won the men's 25-kilometer open water race on Saturday, giving host Italy its first gold medal of the swimming world championships.
Swimming through large waves, Cleri pulled away from Australia's Trent Grimsey in the final kilometer.
Cleri clocked a 5 hours, 26 minutes, 31.6 seconds in the sea course off Rome's ancient port of Ostia.
Grimsey took the silver medal, 19.1 seconds behind, and Vladimir Dyatchin of Russia was third, nearly three minutes back, for his fifth medal at worlds.
Angela Maurer of Germany won the women's race in 5:47:48. Anna Uvarova of Russia took silver, touching 3.8 seconds later, and Federica Vitale of Italy was third, 4.7 seconds back.
It was Maurer's fourth medal at worlds, but her first gold.
At times, swimmers had to dive through high waves or risk being driven back to the beach. Boats bobbled up and down in the surf and many competitors removed their swim caps to deal with severe heat.
Alex Meyer of the United States received a red card and was disqualified for swimming over the legs of a female swimmer.