A statement from World Triathlon confirmed the decision to postpone was made after tests at 02:30 BST on Sunday – just under five hours before races were due to begin.
“The latest tests show a decrease in water quality in the river following the rain episodes over the last two days,” the statement read, external.
“As a result, the water quality at the competition venue on Sunday, 1 September is not suitable for swimming and above the threshold established by World Triathlon.
“It has been decided to schedule all 11 Para-triathlon medal events on 2 September. This is subject to the forthcoming water tests complying with the established World Triathlon thresholds for swimming.
“Paris 2024 and World Triathlon reiterate that their priority is the health of the athletes and with these conditions, the Para-triathlon events cannot take place today.”
Great Britain has 11 athletes competing across seven of the triathlon events at the 2024 Paralympics.
These include reigning PTS5 women’s Paralympic champion Lauren Steadman, who is set to defend her gold against team-mate Claire Cashmore.
The world, European and Commonwealth champion Dave Ellis will look to finally win Paralympic gold in the men’s PTVI, while Rio 2016 silver medallist Alison Peasgood will try to go one better in the women’s PTVI.