Athletes competing in the upcoming Olympic marathon swimming events repeatedly face training delays due to water quality issues in the River Seine.

Paris Olympics organisers said that training for open water swimming in the River Seine had been cancelled due to pollution, raising questions over why triathletes were allowed to use the waterway the day before.

The decision is the fifth time organisers have scrapped training in the river since the start of the Olympic Games on July 28 and is likely to frustrate marathon swimming competitors who must get used to the Seine’s strong currents.

A statement from World Aquatics and the organising committee early on Tuesday said that one out of four readings for enterococci bacteria in the river – an indicator of the presence of faecal matter – was above the upper authorised limit.

“This decision [to cancel training] has been taken out of an abundance of caution, especially given that another familiarisation swim is scheduled for the following day August 7,” it said.

Ever since the River Seine was chosen as a location for the triathlon and marathon swimming, French authorities have been in a race against time to clean up the waterway.

The triathlon was badly disrupted by poor bacterial readings last week, with all swim training sessions cancelled and the men’s individual race postponed by 24 hours until Wednesday.

A mixed relay race also looked in doubt on Monday, but eventually took place on schedule, with Germany clinching gold in a thrillingly close race that saw the USA and Britain win silver and bronze medals.

Marathon swimming – a 10km (6.2-mile) race in open water – is set to take place on Thursday for women and Friday for men.

Organisers have said that marathon swimming can be moved to another location in Vaires-sur-Marne on the River Marne east of Paris if the Seine is too polluted to use.

They said Tuesday that they were “very confident” that the men’s and women’s events would take place in the Seine.