Water aeration is the process of increasing the oxygen saturation of the water. Dissolved oxygen (DO) is a major contributor to water quality. Not only do fish and other aquatic animals need it, but oxygen breathing aerobic bacteria decompose organic matter. When oxygen concentrations become low, anoxic conditions may develop which can decrease the ability of the water body to support life.
Adding an air pump with an air stone in the bottom of your reservoir will increase the dissolved oxygen, dechlorinate the water, and prevent anaerobic bacteria from growing.