Many didn't like what they saw.
"I've been sailing all over the world for 20 years now, and this is the most polluted place I've ever been," said Allan Norregaard, a Danish bronze medallist in the 2012 London Olympics. "It's really a shame because it's a beautiful area and city, but the water is so polluted, so dirty and full of garbage."
Rio's local Olympic organizing committee has promised the pollution will be cleaned up when the Olympics open in 2 1/2 years. Government officials have pledged to reduce 80 per cent of the pollution flowing into the bay.
But the sailors doubt the problem can be fixed after festering for decades, and many worry about their health. Environmentalists call measures being taken "stopgap," likely to mask the problem and not cure it.
The Associated Press has documented over the last several weeks that nearly 70 per cent of Rio's waste goes untreated into surrounding waters. Famous beaches like Copacabana and Ipanema are dirty. Untreated sewage pours into a lagoon bordering the Olympic Park, the heart of the games.
Norregaard said that while sailing the last few days he'd seen entire trees floating in the bay, doors, chunks of timber with nails protruding, swollen mattresses and endless plastic bags.
Another sailor talked about a horse carcass in the 148-square-mile bay, which opens into the Atlantic just above Rio's famed Copacabana beach.
The Dane said the floating debris makes racing unfair and dangerous. The other issue is the health risk with high levels of fecal coliform bacteria in the water.
"I would definitely not swim in it," Norregaard said. "We have had a couple of incidents where people went in the water and came up with red dots on their body. I don't know what's in the water, but it's definitely not healthy."
Brazilian sailor Martine Soffiatti Grael grew up on the bay. Her father, Torben Grael, is a five-time Olympic medallist , two of them gold.
"For me since I was a child, it has only gotten worse," said the 22-year-old, who hopes to qualify for the Rio Games. "The government says it has lots of programs to clean the bay, but I haven't seen any progress being made."
Thomas Bach, the new president of the International Olympic Committee, is scheduled to be in Rio early next year to monitor progress. The IOC is concerned about delays in organizing and building venues, and pollution is another worry with costs for the games put at $15 billion — a mix of public and private money.
"Of course, the water will not be clean as sailing in the Caribbean," Brazilian Robert Scheidt, who has won five Olympic medals, said by phone to the AP. "I have never swum in there (Guanabara). ... Inside the bay I know it's not the proper place to swim. I've sailed there and never got any disease."
Ian Barker, who won a silver medal for Britain in the 2000 Olympics and now coaches Ireland, said he's sailed in 35 countries, and this is the worst. He said sailors in training have had to stop to disentangle their rudders from rubbish.
"It's a sewer," he said. "It's absolutely disgusting. Something has to be done about it. But you need the political will for these things to happen and at the moment it's not there."
Follow Stephen Wade at http://twitter.com/StephenWadeAP