The men’s Olympic triathlon planned for Tuesday has been postponed over concerns about water quality in Paris’ Seine River, where the swimming portion of the race was supposed to take place.

Organizers said they will try to hold the men’s triathlon Wednesday instead. The women’s competition is also scheduled on Wednesday, but both are subject to water tests. Friday is also planned as a backup date.

But Meteo-France, the French weather service, was forecasting storms Tuesday night, light rain Wednesday afternoon and storms Thursday, which could complicate rescheduling the events.