Olympic sailing began an 11-day regatta on Monday with near perfect winds as competitors showed little fear of heading back into waters criticised for sewage-borne pathogens and floating garbage.
Britain's Nick Dempsey scored victories in the first two races in the RS:X class on the Escola Naval course on Guanabara Bay. With winds blowing 10 to 11 knots and strengthening to 14 after the 1:05pm (16.05 GMT) start, Dempsey grabbed large early leads in both races and was rarely challenged.
In the third race Dempsey came in second behind Dorian Van Rijsselberge of the Netherlands, but leads his class after the first day.
''Obviously water quality was an issue,'' said Lindsey Bell, spokeswoman for the British Sailing Team.
''We are taking health precautions but they are the same precautions we take everywhere else and the sailors are excited about sailing here.''
The RS:X women's class also sail three races on Monday. The Men's Laser one-man dinghy and women's Laser Radial classes have two races planned.
Dempsey and others have trained extensively in Rio over the last few years with little or no ill effects, said Bell. Water quality also appears to have improved with strong efforts to clean up debris that could slow or damage boats.
Sailors are more concerned with keeping ahead of Rio's shifting winds and tricky currents and tides.
''The courses are quite a challenge,'' said Marko Misura, team leader for Croatia.
''You have to be an all-around sailor. I don't see any one sailor dominating a class. I see most medals being decided in the medal race.''
Racing will take place in 10 classes: five men's classes, four women's classes and one mixed class. The 324 qualified competitors from 63 countries will compete over 11 days.
All classes will race either 10 or 12 fleet races with each boat receiving points equal to their finish position. At the end of the fleet races the 10 boats with the lowest point totals will compete in a medal race where points are doubled for each position at the finish.
The top three boats after the medal round win gold, silver and bronze.
