The decision came as a relief for the athletes expecting to compete and for Paris authorities who have promised residents a swimmable Seine as a long-term legacy of the Games, with the triathlon a very public test.
"The results of the latest water analyses, received at 3.20am, have been assessed as compliant by World Triathlon allowing for the triathlon competitions to take place," Paris 2024 and World Triathlon said in a statement.
Fifty-five women representing 34 countries will kick off the contest at 8am (6pm NZ time), including New Zealanders Ainsley Thorpe and Nicole van der Kaay.
The men's event will take place at 10:45am (8.45pm NZ time), immediately after the women's race.
New Zealanders Dylan McCullough and medal contender Hayden Wilde are among the men's field.
"It is with great joy that we received this news," Benjamin Maze, technical director for France's triathlon federation, told Reuters.
"Now that we know we will race, we can mentally switch fully into competition mode."
Paris has spent 1.4 billion euros (NZ$2.56 billion) of public money on wastewater infrastructure to contain sewage and minimise spillage into the river, and Mayor Anne Hidalgo took a dip earlier this month in a bid to convince doubters that the water will not make them ill.
The gamble that the river would be clean enough for the triathlon was never guaranteed to pay off as water quality varies widely day-to-day, with rainfall causing concentrations of infection-causing bacteria like E. coli to rise.
