Biochemical oxygen demand in rivers

Biochemical oxygen demand (BOD) of water bodies is a key indicator to measure water quality. It refers to the amount of oxygen that aerobic microorganisms need to decompose organic substances in a water sample over a five-day period at 20 °C (BOD5). High BOD5 values usually indicate organic pollution, which affects water quality and the aquatic environment. Organic pollution caused by discharges from wastewater treatment plants, industrial effluents and agricultural run-off increase BOD. The cleanest rivers have a five-day BOD of less than 1 milligram per litre (mg/L). Moderately polluted rivers show values ranging from 2 to 8 mg/L. Data presented in this section stem from the EEA Waterbase database on the status and quality of Europe's rivers.