Spirit Reservoir Water Quality

Spirit Reservoir is located in a forested watershed with a moderate, but increasing amount of shoreline development, i.e., year-round homes. WVIC owns over 600 acres of forest, located primarily in the upper (west) end of the reservoir, which remains largely undeveloped. Spirit has 1,698 acres of surface water, 55 miles of shoreline and is dotted with several islands. It is relatively shallow, with a maximum depth of 25 feet. The reservoir contains many substrate types, including sand, gravel, boulders and organic muck.

Many wetlands drain into the reservoir which contribute significantly to its dark "coffee" stained water color. The dark water, combined with relatively low transparency (light penetration), low nutrients, such as phosphorus, and low alkalinity (very "soft" water) limit the productivity in the reservoir and therefore the amount of algae and aquatic plants. Spirit has the lowest density of aquatics of the five man-made reservoirs.

The water has very low turbidity. pH generally falls within the acceptable range of 6.0 to 9.0. Surface water temperatures reflect the northern temperate climate and range from 32° F in the winter to 81° F in the summer. Ice thickness can exceed 30 inches in the winter. Dissolved oxygen is good throughout the reservoir. The reservoir weakly stratifies in the summer and strongly in the winter, which is typical of many northern Wisconsin lakes. During stratification, oxygen depletion occurs on the bottom 3-6 feet of the reservoir. This natural occurrence does not adversely affect the Spirit Reservoir fishery.