What specific indicator parameter suggests organic pollution in surface water?

Several indicator parameters can suggest organic pollution in surface water, but Biochemical Oxygen Demand (BOD) is a primary indicator. BOD measures the amount of oxygen consumed by microorganisms as they decompose organic matter in a water sample over a specific period (typically 5 days). A high BOD value indicates a large amount of biodegradable organic material is present, which consumes dissolved oxygen as it decomposes. This oxygen depletion can harm aquatic life, as many organisms require dissolved oxygen to survive. Other indicators of organic pollution include Chemical Oxygen Demand (COD), which measures the total amount of oxygen required to chemically oxidize all organic compounds (both biodegradable and non-biodegradable), and Total Organic Carbon (TOC), which directly measures the amount of carbon in organic compounds. While COD and TOC provide valuable information, BOD is particularly indicative of the readily biodegradable organic matter that directly impacts dissolved oxygen levels in surface water. The ratio of BOD to COD can be used to estimate the biodegradability of the organic matter. Low dissolved oxygen levels in conjunction with high BOD are strong indicators of organic pollution.