Explanation : Biochemical Oxygen Demand (BOD) is a measure of the quantity of oxygen used by microorganisms in the decomposition of organic matter. If a lake is contaminated with polluted water that has high BOD, it means there is a lot of organic matter in the water for bacteria to decompose. During this decomposition process, the bacteria consume oxygen. This leads to a decrease in the amount of dissolved oxygen (DO) in the water. When oxygen levels in the water are depleted, aquatic organisms, especially fish and macroinvertebrates that rely on higher oxygen levels, may die or move to areas with higher oxygen levels. Hence, this form of water pollution can lead to significant changes in the ecosystem.