Water in the Seine River had unsafe elevated levels of E. coli less than two months before swimming competitions are scheduled to take place in it during the Paris Olympics, according to test results published yesterday.
Contamination levels in the first eight days of June, after persistent heavy rain in Paris, showed bacteria such as E. coli and enterococci beyond limits judged safe for athletes.
The report was published by monitoring group Eau de Paris one day after a senior International Olympic Committee executive said there were "no reasons to doubt" races will go ahead as scheduled in in a historic downtown stretch of the Seine near the Eiffel Tower.
The first Olympic event in the cleaned-up Seine is men's triathlon, including a 1.5-kilometre swim, on the morning of July 30.
The women's triathlon is the next day and a mixed relay event is on August 5.
Marathon swimming races over 10 kilometres for women and men are scheduled on August 8 and 9, respectively, in waters that were historically polluted before a $1.5 billion investment ahead of the Olympics.
"We are confident that we will swim in the Seine this summer," IOC official Christophe Dubi said on Thursday at an online briefing after hearing an update Paris from city officials and Olympic organisers.
Despite the IOC's publicly expressed confidence, the final decision on approving the events safe for athletes should rest with the governing bodies of individual sports, World Aquatics and World Triathlon.
The safety of the Seine water for the Olympics has been in doubt since some test events scheduled last August were cancelled, also after unseasonal heavy rains.
According to European standards, the safe limit for E. coli is 900 colony-forming units per 100 millilitres.
The World Triathlon Federation uses the same criteria to determine sufficient water quality for competitions.
During the first eight days of June, test results showed that E. coli levels frequently exceeded these thresholds. Enterococci levels were better, mostly staying within safe limits.
The tests indicated an improvement, from high contamination levels on June 1 to more acceptable levels by June 9, mainly due to improved weather.
Rainwater infiltrates the sewer system, and to prevent street flooding, the excess water, carrying fecal bacteria, is diverted into the Seine.
To address this, a massive reservoir capable of storing 50,000 cubic metres of water during heavy rainfall was inaugurated in May.
Water quality of rivers in major cities can be impacted by many things, from runoff to dumping of chemicals, sometimes illegally, and boat traffic.
Earlier this week, Paris' mayor Anne Hidalgo doubled down on her promise to take a dip in the river before the start of the competition.
On Tuesday, she confirmed that her swim was postponed until after the snap elections in France, which end on July 7.