Faecal contamination of the Seine, which winds 777 kilometres through northern France, exceeded the bathing quality standard for safe swimming just two days before the men’s and women’s triathlon races. Athletes testing the waters before making the plunge to compete have become accustomed to such setbacks. Just a year earlier, the open-water swimming world cup and the para triathlon test event and mixed relay competition in the Seine were cancelled due to the low quality of the water. No wonder athletes were worried ahead of Paris 2024.
The Seine is burdened with an enormous population (12.3 million people live in the region surrounding Paris) and a low river flow that cannot easily dilute pollution. A 19th-century combined sewer system is expected to manage a lot of wastewater: rainwater flows over roads, fields and rooftops and enters the sewer system, accumulating oil, heavy metals, animal faeces and pesticides along the way.
Combined with untreated sewage from homes and businesses, sewer water flow often strains the capacity of the network and treatment plants. To prevent backflow, untreated wastewater is discharged into the Seine through 200 outlets. This is commonly known as a combined sewer overflow.
The result is a murkier river with less oxygen dissolved in it and a higher concentration of faecal bacteria. During one intense rainstorm, the level of E coli and Enteroccus bacteria discharged into the Seine from one outfall rose nearly 100 times compared to a dry weather period.
Climate change could degrade the river further. Regional-scale climate models project more short and sharp downpours during the summer. The years 2016, 2022, 2023 and now 2024 have all seen heavy rainfall during June and July.
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For the full article by Jamie Wilks and Lois Mougin visit The Conversation.
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