As Paris opened the 2024 Summer Olympic Games along the Seine River, it was easy for many to fall in love with the romantic waterway and forget what lies beneath.

But the steady rain this past Friday was a reminder of how the weather impacts the river’s water quality.

Organizers canceled the practice run for the upcoming triathlon on both Sunday and Monday due to concerns that the heavy rains negatively impacted the water quality, according to multiple reports.

LISTERIA INFECTION LINKED TO DELI MEATS KILLS 2, INFECTS 28 ACROSS US, CDC WARNS

Officials were still optimistic that warmer temperatures would reduce the bacteria levels so the men’s triathlon could proceed as planned on Tuesday — but the race was ultimately postponed.

"Despite the improvement in the water quality levels in the last hours, the readings at some points of the swim course are above acceptable levels," the World Triathlon said in a statement on X.

Experts from University of Florida (UF) Health, a member of the U.S. Olympic & Paralympic Medical Network, discussed with Fox News Digital how the Seine River could impact athletes’ health.

IN COLORADO, PLAGUE CASE CONFIRMED IN HUMAN, HEALTH OFFICIALS SAY: ‘MUST BE TREATED PROMPTLY’

The quality of water may vary depending on the time of day and the number of infectious particles consumed, Kartikeya Cherabuddi, M.D., professor of infectious diseases and global medicine at the University of Florida, told Fox News Digital.

"Taking precautions and being aware of potential symptoms so they can be managed early is important," he said.

For the past 100 years, swimming has been illegal in the Seine River due to poor water quality — with the exception of rare competitions, according to multiple reports.

"The city of Paris has put a great deal of effort into cleaning up the Seine," Nicole Iovine, M.D., Ph.D., chief epidemiologist and chief quality officer at UF Health, told Fox News Digital.

"[As in] many old cities, both sewage and storm runoff travel in the same pipe that is destined for water treatment plants," she said.

"If there are heavy rains, the pipe capacity can be overwhelmed, and the excess can end up in the Seine."

ON THIS DAY IN HISTORY, JULY 20, 1968, FIRST SPECIAL OLYMPICS SUMMER GAMES ARE HELD IN CHICAGO

To prepare for the Olympics, the city spent $1.5 billion to build an underground storage basin, called "Austerlitz Basin," along with a renovated sewer system and upgraded treatment plants.

The goal was for the improved system to collect excess rain to prevent wastewater from flowing into the Seine, according to a recent report.

Heavy rains, however, could thwart those efforts.

About one week before the Olympic Games, Paris Mayor Anne Hidalgo took a highly publicized dip on July 17 to show that the waters were safe for the triathlon and marathon events.

Later testing, however, revealed that in some areas, levels of E. coli bacteria were above Europe’s maximum safety limit, which is 900 colony-forming units per 100 milliliters.

One person swimming in the river doesn’t prove that the water is safe, experts pointed out.

"The risk of aspirating river water is much greater when engaged in a highly exertional activity like a competitive race compared to a more leisurely dip in the Seine," Iovine said.

Eau de Paris, the largest public water company in France, found that the Seine’s water quality for the week of July 17 "reached the compliance thresholds of the European directive at all four points monitored over four days," according to the city’s website.

DIVERS DISCOVER 19TH CENTURY SHIPWRECK CONTAINING HISTORICAL ARTIFACTS IN BALTIC SEA

The water is tested early each morning during the Olympics to ensure that the events can proceed as planned, officials say. 

The tests typically screen for certain types of bacteria called total coliforms, and generally do not look for other germs, like viruses and parasites, Iovine noted.

Most coliforms, which are found naturally in the environment as well as in human and animal waste, are not harmful — and the ones that can cause illness are usually present in low amounts that don’t pose a threat, he said.

High levels of coliforms, however, can be a marker of excessive fecal matter, which can make people sick, according to experts.

"If the amount of coliforms increases, that could be because significant numbers of pathogenic bacteria, like E. coli, have entered the water, making it potentially unsafe," Iovine warned.

E. coli (Escherichia coli) is a group of bacteria in the intestinal tract that helps to digest food and protect the body from harmful germs, according to the Centers for Disease Control and Prevention (CDC).

Some types, however, can cause illness.

People can get infected by swallowing water that is contaminated with the waste of an infected person.

Common bacterial symptoms include watery or bloody diarrhea, severe stomach cramps, and vomiting that may be associated with a fever, according to the CDC.

WATER SAFETY TIPS FROM EXPERTS FOR FAMILIES AND CAREGIVERS AS DROWNING DEATHS INCREASE

Other bacteria associated with sewage, such as Enterococcus, Salmonella and Campylobacter, can cause a similar array of infections, Iovine warned.

"I am concerned that if the level of harmful bacteria is too high, the athletes [could be] at risk for contracting gastrointestinal illness," she said.

Skin and eye infections are also possible if people have small nicks or abrasions on their skin before entering the water.

Parasites, like Giardia, amoebas and Cryptosporidium — and viruses, such as norovirus, hepatitis A and hepatitis E — may also be present in human and animal sewage, Iovine added.

Symptoms of viruses and parasites are predominantly stomach-related, such as nausea, vomiting, diarrhea and abdominal pain, but can also include fevers, headaches, and respiratory or urinary issues, Cherabuddi noted.

"Symptoms may start within one to two days, but could present a week or two later," he added.

CLICK HERE TO SIGN UP FOR OUR HEALTH NEWSLETTER

Harmful pathogens carried by rodents can also enter the river with overflow from rainwater, Iovine said.

The urine of rodents, for example, can contain bacteria called Leptospires, which can cause a bacterial disease called leptospirosis. 

That condition can cause nausea, vomiting, body aches, red eyes, fever and headache, according to Iovine.

"Since these athletes are young and healthy, I would expect them to recover from these infections if they occurred, but it could impact their ability to compete in their events if they are sick," she said.

For more Health articles, visit www.foxnews/health

Athletes who are immunocompromised may experience more severe illness than those with healthy immune systems.

Fox News Digital reached out to the International Olympics Committee and Eau de Paris requesting comment.