Definition - What does Oxygen Sag mean?
Oxygen sag or the oxygen sag curve refers to the reduction in dissolved oxygen plotted over a distance along a water body from a point at which sewage or other pollutants have been discharged. The phenomenon of oxygen sag is usually related to the release of organic pollutants or nutrient elements, which promote the growth of oxygen-consuming micro-organisms.
Safeopedia explains Oxygen Sag
Oxygen sag is a key indicator of water quality and the effects of pollution. The EPA provides guidelines for the determination of water quality including procedures for field measuring techniques. Low levels of dissolved oxygen impact aquatic life and indicate the presence of eutrification, a condition in which there is an overgrowth of certain organisms, causing poor oxygenation owing to the resulting ecological imbalance.