Summertime hypolimnetic anoxia is a common phenomenon in productive drinking water reservoirs. It can result in a number of negative environmental consequences. Anoxic sediment tends to release ammonia and orthophosphate, a phenomenon known as internal nutrient loading, which can reinforce eutrophication (Broström et al. 1988, Ahlgren et al. 1994). Entrainment of nutrients from the hypolimnion to the epilimnion can support summer blooms of blue-green algae which may produce objectionable and difficult-to-remove taste and odor compounds. Anoxic conditions can also lead to hypolimnetic accumulation of iron, manganese and sulfides that can degrade the aesthetic quality and treatability of drinking water (Sartoris and Boehmke 1987). Elevated concentrations of toxins (e.g., sulfide and ammonia (in the hypolimnion as a result of anoxia may impair aquatic biota within the reservoir and in tail-waters released from the hypolimnion (Cooper and Koch 1984, Horne 1989). Finally, anoxic conditions may also increase mercury contamination in lake biota by stimulating the release of methylmercury from sediment (Herrin et al. 1998).