The biochemical oxygen demand (BOD) represents the amount of dissolved oxygen (DO) consumed by biological organisms when they decompose organic matter in water. The chemical oxygen demand (COD) is the amount of oxygen consumed when the water sample is chemically oxidised.
BOD and COD can reduce the DO of lakes and rivers, and low concentrations can cause eutrophication and harm aquatic life.
Municipal wastewater discharge and industrial processes can create water high in COD/BOD, requiring careful treatment before discharge to preserve the health of waterways.