On a rainy morning, the Olympic triathlons kicked off with the women diving into the Seine River after days of delays due to water quality concerns.

Starting near the iconic Pont Alexandre III, the drizzle eased as the athletes entered the water, with the Eiffel Tower providing a striking backdrop.

Some triathletes dipped their goggles into the Seine before donning them and starting their swim.

The decision to proceed with the swim is a significant victory for the city, Olympic organizers, and the athletes.

Officials implemented an ambitious plan, including 1.4 billion euros ($1.5 billion) in infrastructure improvements, to clean up the long-polluted Seine.

They have been adamant that the swimming portion of the triathlon and next week’s marathon swimming events could be held safely in the river.

Organizers said early Wednesday that the latest water tests met quality standards, though early morning rain could have affected those results.

"The problem is always worse with heavy rainfall because it overwhelms the pipes and causes runoff from the streets to enter the Seine," explained Dr. Nicole Iovine, an infectious diseases specialist at the University of Florida. "They’ve done a lot to improve water quality, but ultimately, you’re at the mercy of Mother Nature."

As they swam, the women stayed close to the barges and boats lining the riverbanks. Spectators watched and cheered from stands along the side and from bridges spanning the waterway. Reigning Olympic champion Flora Duffy of Bermuda was the first out of the water, completing the 1.5-kilometer course in about 22 minutes.

After swimming two laps in the Seine, the athletes ran up a set of stairs to transition to their bikes for a ride through the rain-soaked streets of Paris, including the iconic Champs-Elysees. Several wipeouts and spills occurred early in the bike race.

Elevated levels of bacteria in the river pushed the men’s race, originally scheduled for Tuesday, to Wednesday, the same day as the women’s competition. The men were slated to start about three hours after the women's race. Test events meant to familiarize athletes with the course had already been canceled for the same reason on Sunday and Monday.

The water quality in the Seine is directly affected by rainfall, which can lead to wastewater runoff into the river. Heavy rains fell during Friday’s Olympic opening ceremony and continued through Saturday.

Even as organizers announced cancellations or postponements, they expressed confidence that the swims would proceed as planned the following day. For several days, they did not publicly release data on E. coli and other bacteria levels that influenced their decisions.

High levels of E. coli can indicate sewage contamination. Most strains are harmless and some live in the intestines of healthy people and animals, but others can be dangerous. Even a mouthful of contaminated water can cause diarrhea and infections in the urinary tract or intestines.

Daily water quality tests measure E. coli levels. World Triathlon’s water safety guidelines and a 2006 European Union directive provide a range from "excellent" to "sufficient." Anything beyond 900 colony-forming units per 100 milliliters is not considered safe. Experts emphasize that these numbers are guidelines used to assess risk.

Aurélie Merle, Paris 2024’s director of sports, said Tuesday that water samples are taken 21.5 hours before decisions are made about the swim, leaving some uncertainty about their accuracy on the day of the race.

Merle noted that testing results showed "we’re very close to the threshold for triathlon." She mentioned that one of four test sites along the triathlon course was below the E. coli threshold, while two sites were just above the limit, and one was more elevated, with levels ranging from 980 to 1,553.

"We know the sun and heat have a strong impact on water quality," she said, hoping that a heat wave affecting much of France on Tuesday would improve water quality enough for the swims to proceed.

Organizers have said that if needed, the marathon swimming races, scheduled for Aug. 8 and 9, could be relocated to the Vaires-sur-Marne Nautical Stadium in the greater Paris region, which already hosts rowing and canoeing competitions and can accommodate up to 15,000 spectators.