Short answers, pulled from the story.
The four main sources of water pollution are sewage discharges, industrial activities, agricultural activities, and urban runoff including stormwater. Sources are classified as either point sources, which have a single identifiable origin such as a pipe or storm drain, or non-point sources, which are diffuse, such as agricultural runoff across wide areas.
A study published in 2017 found that polluted water killed 1.8 million people that year by spreading gastrointestinal diseases and parasitic infections. Persistent exposure to water pollutants also increases the risk of cancer and other long-term diseases.
Thirty-five percent of all ocean microplastics come from textiles and clothing, primarily through the erosion of polyester, acrylic, and nylon fabrics during washing. Synthetic fabrics, tyres, and urban dust together account for over 80% of all microplastic contamination, with the main transport routes to the sea being stormwater, untreated sewage, and wind.
Eutrophication is an increase in chemical nutrients in an ecosystem that boosts primary productivity, typically through algae blooms. Nitrogen and phosphorus pollution from sewage and agricultural runoff are the main drivers, and the resulting oxygen depletion, known as anoxia, can kill fish and severely reduce water quality.
Water pollution is measured using physical methods such as temperature, turbidity, and conductivity tests; chemical analysis of parameters including pH, dissolved oxygen, and metals such as mercury, lead, and cadmium; and biological monitoring using indicator organisms such as fecal coliforms including Escherichia coli as proxies for dangerous pathogens.
High levels of sewage in the River Seine forced organizers to delay several swimming-focused events at the 2024 Paris Olympics, including the triathlon. The episode highlighted ongoing failures in water quality even in countries with established environmental regulation.