Winchester Lake To Receive Aeration System

WINCHESTER - Catching fish at Winchester Lake will likely be improved as the Idaho Department of Fish and Game, Department of Environmental Quality and the Winchester Watershed Advisory Group plan to install a water aeration system to improve water quality at the popular, 75-acre reservoir, located 30 miles southeast of Lewiston. "Because of warm water temperatures, high levels of phosphorus and low dissolved oxygen levels, fish can only survive in a small portion of the reservoir," said Regional Fisheries Biologist Robert Hand. "This aeration system will be life-support for cold-water fish." During the spring and summer months, sunlight and warm air temperature heat the surface water of a lake. Cold water, due to its higher density, is heavier and sinks to the bottom, creating a condition called thermal stratification in which the warm and cool layers of water don't mix. In addition, sunlight warms the surface water, allowing tiny plants to grow. As the plants die and sink, their decomposition uses up the oxygen in the deeper cool water, referred to as the hypolimnion. Throughout the summer, oxygen levels in the deeper water continue to decline until no oxygen is present. This oxygen depletion, combined with warm water in the lake's upper layers, reduces the volume of the water in the lake that can support cold-water fish to less than 16 percent of the total lake volume. Additionally, these periods of no oxygen allow the release of phosphorus from lake sediments into the waters of the hypolimnion. During the fall, colder air temperatures cool the lake's surface waters. When the surface water becomes cooler than the deep water, the surface water sinks and the lake "turns over". This turnover allows the high concentrations of phosphorus in the hypolimnion to mix throughout the lake. The lake is thus fertilized for abundant plankton growth to occur the next summer and the cycle is repeated. Seven aeration units will be placed in the deeper portions of the lake. This system takes water from the bottom of the lake, bringing it to the surface where it is oxygenated by contact with air, then it is returned to the bottom of the lake. A compressor releases air at the bottom of a vertical pipe. As the air rises, it forces water up the pipe into an attached trough. As the level of the water increases in the trough, gravity forces water back down a second pipe to the bottom of the lake. By increasing the level of oxygen in the lower water layers, the amount of phosphorous released into the water is reduced, thus reducing the amount of "fertilizer" available for algae. This in turn reduces the loss of oxygen, thus breaking the cycle. This lake project is in conjunction with a project designed to improve water quality in the watershed above Winchester Lake. Funds used are from a federal government Clean Lakes Act Grant.