Why has pollution made some Danube River water unsuitable for drinking and irrigation?

The Danube River has become nearly unfit for both drinking and irrigation due to a tremendous increase in pollutants. This degradation is primarily driven by the discharge of untreated city sewage and industrial chemical wastes into the river as it flows past urban and industrial centers.123

Additionally, the river’s water quality is compromised by agricultural runoff, which introduces fertilizers—specifically phosphates and nitrates—into the system. These chemicals can trigger eutrophication, a process that promotes excessive algal growth and oxygen depletion, further rendering the water unsuitable for human consumption without specialized treatment. The cumulative effect of these diverse pollutants has not only impacted water utility but has also diminished the river's once-rich fishing grounds.231