Understanding the issue with Seine water quality – Technologist

Swimming has been off-limits in Paris’ Seine River for more than a century. So with Olympic swimming events on tap for the river, the city poured in €1.4 billion to try to clean it up. With the Paris Games underway, officials are keeping a close eye on water quality. Athletes could feel health effects from swimming in a river with higher-than-accepted levels of E. coli or other bacteria.

What made the Seine so dirty?

Paris, like many old cities around the world, has a combined sewer system, which means that the city’s wastewater and stormwater flow through the same pipes. With heavy or prolonged periods of rain, the pipes can get overwhelmed and untreated wastewater flows into the river instead of to a treatment plant. That could mean bacteria, viruses or parasites get in the water.

What did Paris do to clean up?

To prepare for the Paris Games, the city built a giant basin to capture excess rainwater and keep untreated waste from flowing into the river, renovated the sewage system and upgraded water treatment plants.

Heavy rain may still swamp the system. The rain over the Olympics opening weekend filled up 20% of the basin, so the contamination levels afterward likely came from wastewater upstream, city officials said.

What germs are in the river?

Water quality tests in June revealed unsafe levels of E. coli bacteria, though results in early July showed improvement. E. coli is found in human and animal digestive tracts and waste. A monitoring group does daily tests at four spots for E. coli as well as enterococci bacteria, which can signal fecal matter and potentially disease-carrying germs.

The World Triathlon Federation has deemed E. coli levels beyond 900 colony-forming units per 100 milliliters are unsafe.

What happens when you swim in contaminated water?

Swimming in water with unsafe levels of bacteria can lead to an upset stomach and intestinal problems. Swimmers may inadvertently swallow the water or pick up infections through open cuts.

Even a mouthful of contaminated water can lead to diarrhea, and germs can cause illnesses such as infections in the urinary tract or in the intestines, or in the worst-case scenario, life-threatening sepsis.