Concentration of dissolved oxygen is dependent on the physical, chemical and biochemical properties of the water. The temperature of the water is the most important controlling variable and has an inverse relationship with dissolved oxygen i.e.dissolved oxygen concentration increases with decreasing temperature. Different aquatic species have different tolerance levels. Fecal contamination may originate from many different sources including sanitary waste water or agricultural runoff. The pH of water is an important quality factor.
Nitrates are present in some fertilizers and in the manure of animals.
The total amount of phosphorous in the water in various types of phosphate compounds. Phosphates may originate from a variety of sources including sanitary wastewater and agricultural runoff. The equilibrium temperature is the temperature which would be reached by the water body in the prevailing weather conditions when totally unaffected by thermal discharge. Water temperature is important because it influences the metabolic rate of aquatic organisms and the rates of chemical reactions. Such heated water may be detrimental to aquatic life, a condition termed thermal pollution.