Is the Seine safe for Olympic competition? On Day 2 of the Games, the answer was no

It's been a topic of conversation for months: Will the Seine be clean enough for swimming after French officials spent more than $1.5 billion US to clean the polluted river?

The answer on Sunday was no. Paris Olympic officials cancelled a pre-race triathlon training event set to take place in the Seine, citing water quality issues after heavy rainfall over the last couple of days.

A senior Olympic official promised the water quality will get better soon, with the first triathlon event set for Tuesday in the Seine.

"We are still very confident," Paris 2024 executive director of communications, Anne Descamps, said on Sunday.

World Triathlon officials also expressed confidence that the river will be safe to swim in by Tuesday, according to The Associated Press.

The Seine was the star of the show at the opening ceremony on Friday. Delegations travelled by boat down the more than 700-kilometre long river that runs through Paris.

That went off without a hitch, but the Seine is also supposed to play host to the swimming portion of the triathlon and open-water marathon swimming, which starts on Aug. 8.

So, what's the problem? There are two main issues at play here, according to Jordan Peccia, who teaches environmental engineering at Yale University.

The first is that the Seine runs through a major city, and when it rains (and anyone who watched the opening ceremony on Friday saw just how much it rained), the water hits non-permeable surfaces like concrete and runs into sewers, which discharge into the river.

But the bigger problem, according to Peccia, is that Paris, like many other old cities, has a combined sewer system where wastewater and runoff are combined.

"It all goes to a wastewater treatment plant and it can all be