Ana Marcela Cunha of Brazil won the women’s 10-kilometer marathon swimming event.
Cunha touched first in 1 hour, 59 minutes, 30.8 seconds on Wednesday morning, finishing nine-tenths of a second ahead of defending champion Sharon van Rouwendaal of the Netherlands.
Van Rouwendaal took silver in 1:59.31.7.
Kareena Lee of Australia earned bronze in 1:59.32.5.
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Cunha won her first medal in her third Olympics. She was 10th five years ago in Rio de Janeiro and fifth in the 2008 Beijing Games.
American Haley Anderson finished sixth and her teammate, Ashley Twichell, was seventh.
The seven-lap course in Tokyo Bay featured a backdrop of skyscrapers, the Rainbow Bridge and the nearby floating Olympic rings.
The air temperature during the latter stages of the race was 86 degrees Fahrenheit (30 Celsius), with 74 per cent humidity that made it feel like 95 degrees (35 C).
The water temperature was about 84 degrees (29 C), under the allowable limit of 88 degrees (31 degrees C).