Dissolved oxygen is an important factor that determines the quality of water in lakes and rivers. The higher the concentration of dissolved oxygen, the better the water quality. When sewage enters a lake or stream, micro-organisms begin to decompose the organic materials. Oxygen is consumed as micro-organisms use it in their metabolism. This can quickly deplete the available oxygen in the water. When the dissolved oxygen levels drop too low, many aquatic species perish.
Similarly an optimum temperature of water is essential, depending on the area, for the organisms to survive. Increase in water temperatures due to human activities make the habitat unsuitable for the aquatic species and also decreases the dissolved oxygen in the water body. Thus greater water temperature indicates water pollution.
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