The world governing body for sailing is expected to announce this week that it is tentatively sticking to plans to hold races in next year’s Summer Olympics inside highly polluted Guanabara Bay, yet will keep the option open to moving the courses.

Although reports of Rio de Janeiro’s polluted waters are intensifying pressure on sports officials to reconsider, the provisional Olympic sailing competition schedule has three of five racecourses inside the bay, the same ones that were used in test events here in August, said the international sailing federation, known as ISAF.

A fourth course inside the bay has been added as a backup.

“This is the competition that we want to happen,” said Alastair Fox, head of competitions for the federation. “But if on any given day we feel like we can’t get in a fair race, we’ll move the course outside the bay.”

The federation will closely monitor the installation of a new sewage pipe in Marina da Gloria, scheduled to be completed by the end of the year. “The marina has always been the biggest headache,” Mr. Fox said.

Once the pipe is built, “we need to start seeing weekly improvements starting at the beginning of next year,” he said.

The decision to release a schedule now, without changes, stems from a desire to give athletes an opportunity to prepare. It was informed by medical data the federation collected from the August test race showing that problems with infection and illness among athletes were not as significant as feared.

A report on the data, which has not been completed, will be presented next month at ISAF’s annual meeting, in Sanya, China.

The group finished collecting raw data last week.

Dr. Nebojsa Nikolic, a member of the sailing federation’s medical commission and its chief medical officer during the August regatta, said Tuesday that among 326 sailors who participated in the study he led, 29 experienced traveler’s diarrhea, a stomach illness also known as gastroenteritis that is often caused by local bacteria.

Six of those 29 cases constituted a cluster and were attributed to eating food at Maracanã stadium while attending an event unrelated to the regatta or water, the results indicated.

Putting aside those six athletes, the rate of illness among sailors was 7.1 percent. Dr. Nikolic said that was “much lower than would be expected,” and within levels considered acceptable. He also said the percentage was significantly lower than the rate among the general population traveling to Brazil.

Final conclusions have not been made yet, and Dr. Nikolic cautioned that “we still don’t know the role of water.” Dr. Nikolic’s preliminary findings influenced the federation’s decision to release its schedule now.

“We were confident from his report and feedback, and so we’ve gone forward with our Plan A,” Mr. Fox said.

ISAF said it was also buoyed by athletes’ experiences in the August regatta. Mr. Fox said that in that competition, according to the group’s data, “not a single boat or any of the foils was damaged,” and “there were no reports at all that anyone’s performance was affected” by any debris in the water.