Biochemical oxygen demand in rivers

Biochemical oxygen demand (BOD) is used to measure water quality. It refers to the amount of oxygen required by aerobic microorganisms to decompose organic substances in a water sample over a period of five days in the dark at 20°C (BOD5), measured as milligrams per litre (mg O2/L) and weighted by the number of measuring stations. High values of BOD5 are usually a sign of organic pollution, which affects the water quality. The cleanest rivers have BOD5 values of less than 1 mg O2/L, moderately and heavily polluted rivers show values ranging from 2 to 8 mg O2/L. Only complete series after inter/extrapolation are presented. For details on the total of measuring stations and their distribution over the countries, please consult the metadata file.