The swimming section of a Para-triathlon test event in Tokyo has been cancelled after high levels of bacteria were found in the water.
Organisers reduced the Tokyo Para-triathlon World Cup to a duathlon - two runs and a bike race - after tests showed levels of E. coli were more than twice the accepted standard.
Great Britain won three golds, three silvers and a bronze medal.
Because of the format change, the GB team will now be selected in October.
Athletes had hoped to qualify for next summer's Paralympics, but were unable to do so as the race did not include all three disciplines.
"Apparently the world triathlon Para-triathlon Paralympic test event in Tokyo is now a duathlon due to poor water quality," tweeted Former British Paralympic swimming gold medallist and Para-triathlete Clare Cunningham.
"A completely different race and puts some athletes at a huge disadvantage racing in their tri classification. Disappointing for all."
Shinichiro Otsuka, managing director of Japan's Triathlon Union said: "I'm so sorry for athletes that we could not prepare the competition conditions effectively. It was regrettable."
Britain's Lauren Steadman won gold in the PTS5 category, with team-mate Claire Cashmore in second.
In the PTVI category, triple world champion Dave Ellis secured gold alongside his guide, three-time Olympian Tim Don.
Commonwealth champion Joe Townsend won Britain's other gold, dominating the PTWC race to win gold.
After the women's triathlon test event on Thursday, French triathlete Cassandre Beaugrand was taken to hospital with suspected heatstroke, despite organisers cutting the run to 5km.
Tokyo 2020 organisers have been testing misting sprays and air-conditioned tents to combat soaring temperatures, after a 2018 heatwave in the city killed more than a dozen people.
The World Triathlon Olympic Qualification mixed relay race takes place on Sunday and will be streamed live on the BBC Sport website.