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Summary

In European rivers, oxygen consuming substances decreased over the period 1992 to 2020. Biochemical oxygen demand (BOD) fell to half of the 1992 level, but remained steady at around 2.5 mg O₂/l since 2010. Ammonium concentrations fell to a 23% of the 1992 level. After 2014, the level stabilised around 100 µg N/l. The decrease in BOD and ammonium concentrations is a consequence of the improvement in wastewater treatment. The 1990s economic crisis in central and eastern European countries also resulted in decreasing pollution from manufacturing industries.