Environmental features, general hydrology, and external sources of nutrients affecting Wilderness Lake, King County, Washington

A water budget prepared for Wilderness Lake, a candidate for lake-quality restoration, indicates that of the 530 acre-feet of water that enters the lake each year, 170 acre-feet is from precipitation and 360 acre-feet is from groundwater inflow. An equal amount leaves the lake, and of this, 380 acre-feet is by surface runoff, 8 acre-feet is by groundwater seepage, and 140 acre-feet is by evaporation. Based on these amounts of inflow and outflow, the theoretical water-renewal time of the lake is calculated to be 2.6 years. The annual contributions of nitrogen and phosphorus to the lake from precipitation, natural ground water, and septic-tank leachate are about 920 kilograms nitrogen and 38 kilograms phosphorus. Nitrogen and phosphorus contributions from other sources were not assessed but could be significant. (Woodard-USGS)