RIO DE JANEIRO—Sailors participating in Rio de Janeiro's first prep event for the Olympics this week say water pollution hasn't affected competition, a major relief for local authorities who are struggling to clean up Guanabara Bay.

With just two years until the Olympic torch makes its South American debut, an international sailing regatta is giving organizers and many athletes a chance to test the bay's waters for the first time. Some say Rio is passing the test.

...