The classification system developed allows a rapid assessment of the eutrophic potential and condition of more than 750 Washington lakes and reservoirs. The potential for nutrient enrichment from natural sources is evaluated on the basis of the interactions of physical and hydrologic factors that play a role in controlling the trophic condition of lakes, such as: (1) mean depth, (2) volume, (3) bottom slope, (4) shoreline configuration ratio, (5) ratio of drainage area to volume, (6) altitude, and (7) water-renewal time. The potential for nutrient enrichment from cultural sources is evaluated on the basis of (1) total phosphorus loading from nonpoint sources and point sources, (2) volume of water per nearshore home, and (3) percentage of shore developed. Total phosphorus loading for the lakes is calculated using criteria based on phosphorus exports from various nonpoint sources in the lake basin. Indicators of eutrophication and water quality are evaluated from phosphorus and nitrogen concentrations, specific conductance, dissolved-oxygen depletion in the hypolimnion, Secchidisc visibility, fecal-doliform bacteria, and the abundance of rooted aquatic plants. The classification system, applied to seven Washington lakes, shows that a high enrichment potential from natural and (or) cultural factors is a good indicator of eutrophication and water-quality conditions for the lake.
