A test session to allow Olympic athletes to familiarise themselves with the open water marathon swimming course was cancelled due to further concerns over water quality in the Seine River.

World Aquatics made the decision to cancel the exercise at an early morning meeting on Tuesday.

Fluctuating bacteria levels in the Seine have been a constant concern throughout the Paris Games with the swimming portion of the triathlon and the marathon swimming events both planned in the river.

Another swimming test event is scheduled for Wednesday, and organisers will decide early whether it will go ahead, a statement said.

The 10km women’s competition is scheduled for Thursday - with Australia represented by Chelsea Gubecka and Moesha Johnson - while compatriots Kyle Lee and Nicholas Sloman are set to race in the men’s race on Friday.

The cancellation of Tuesday’s test comes a day after the triathlon mixed relay event was held in the river.

Four triathletes - of the more than 100 who competed in the men’s and women’s individual races last week - became sick in the following days after those events, though it’s unclear whether the water was to blame.

Heavy rainfall last week increased the levels of harmful bacteria in the Seine, although hot weather can reduce the amount.