Open water swimming at the World Championships in Singapore has been postponed because of “water quality levels exceeding acceptable thresholds,” governing body World Aquatics said in a statement.

The fixtures, which were to begin with a women’s 10-km event on Tuesday, have been postponed by a day. The men’s 10-km event will also be held on Wednesday. Other open water events are scheduled for Friday, Saturday and Sunday.

Open water swimming was an issue in last year’s Olympics in Paris as well with concerns raised about water quality in Seine River. It was also an issue at the Tokyo Olympics in 2021 and the 2016 Olympics in Rio de Janeiro.

Water polo competition at the World Championships is underway at an indoor venue. The main event of the championships is eight days of swimming competition in the pool, which begins on July 27.