This report presents comparisons and a graphical overview of the relative magnitude and the regional and statewide distribution of 19 selected cultural, physical, and water-quality characteristics measured in a reconnaissance study of several hundred lakes in Washington. The selected characteristics presented for each lake include types of land use in the lake drainage basin, shoreline residential development, altitude of lake, mean lake depth, nitrogen and phosphorus concentrations in upper and bottom waters, specific conductance, temperature and dissolved-oxygen concentration cf bottom water, Secchi-disc visibility, emersed macrophytes covering shoreline and lake surface, and fecal-coliform bacteria.
Statewide, about two-thirds of the lake drainage basins studied have more than half their land in forest. Urban and suburban developments of the basins are highest in the more populated western Washington counties near Puget Sound, whereas most land in the drainage basins of lakes in the Columbia Plateau of eastern Washington is used for agricultural purposes. Statewide, almost one-fourth of the lakes are shallow (mean depth 2.0 meters or less) and only 7 percent of the lakes have mean depths greater than 20 meters. Dissolved-oxygen layering in summer was detected in many lakes throughout the State. The oxygen concentrations in the upper waters of these lakes were typically near saturation, but the bottom waters of many were severely depleted. Statewide, about one-third of the lakes had Secchi-disc readings of 2.0 meters or less, a value often considered characteristic of eutrophic lakes. The poorest water clarity was observed in the Columbia Plateau, where 68 percent of the lakes had Secchi-disc readings of less than 2.0 meters. Statewide, the median concentration of total phosphorus in the upper waters of lakes was 20 micrograms per liter. More than one-third of the lakes in the State had total phosphorus concentrations in their upper waters that exceeded 30 micrograms per liter, a concentration that is often considered characteristic of eutrophic lakes.
