Punishing heat and stinky water put off swimmers big-time at a test event in Tokyo Bay for the 2020 Games, with one entrant saying parts of the course smelled like a toilet.

After several days of 35-degree heat in the capital, the start time for the Aug. 11 open water event off the Odaiba waterfront district was changed from 10 a.m. to 7 a.m. for men, with women due to start at 7:02 a.m., in light of concerns about rising water temperatures.

The International Swimming Federation (FINA) sets an upper limit of 31 degrees for water temperature to minimize the health risk to athletes.

As of 5 a.m. on Aug. 11, the water temperature was 29.9 degrees.

“It was grueling,” said a female swimmer after finishing the 5-kilometer race. She added that she was concerned she might suffer heat stroke due to the high water temperature and scorching sun.

The 10-km circular course event is currently scheduled to start at 7 a.m. for men and women in next year's Olympics, which run from July 24 to Aug. 9.

However, FINA’s executive director, Cornel Marculescu, indicated that the start time for the race could be moved forward to between 5 a.m. and 6:30 a.m., depending on the water temperature.

He said a decision on when to start will be made after all options are considered.

Improving the water quality is another challenge facing Olympics officials.

"To be honest, it smelled bad," a male swimmer said after emerging from the course. "It smelled like a toilet."

He added that it is important for athletes not to be affected by their surroundings, especially given that they have been assured germs in the water are within the safety limit.

Before the preparation event, the organizing committee for Tokyo Olympics hung a 400-meter-long protective sheet in the water to keep Bacterium coli from entering the venue from the sea.

The Tokyo metropolitan government tested the water quality last summer by using three such barriers. It found that levels of Bacterium coli in the venue were below the safety limit.

In the bay outside of the protected area, Bacterium coli levels were found to exceed the standard for five of the 22 examination days.

Three barriers are expected to be put in place during the Games.

"We believe that we can secure safe water quality by using them," said an organizing committee official in charge of the event.

"Other than that, all we can do is hope that heavy rains or a typhoon that causes the inflow of Bacterium coli do not hit around the day of the race."