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Standley Lake is a reservoir that provides water to several suburban cities in Jefferson County, northwest of Denver, Colorado. In 1988, a taste and odor problem developed in water supplied from the lake. In 1989, a study was begun to determine the nutrient availability in the lake, the potential nutrient limitation to algal biomass, and the occurrence and potential sources of compounds that cause taste and odor problems in water withdrawn from the lake. Physical, chemical, and biological water-quality data were collected during June 1989 through October 1990 from sites in the lake, its primary inflows, and its outflow. Standley Lake was thermally stratified from June through September each year of the study and was well mixed during October-December and March-May. Nutrient concentrations were low in the photic zone. Total nitrogen generally was less than 0.3 milligram per liter and total phosphorus always was less than 0.02 milligram per liter. Concentrations were higher in the hypolimnion, particularly during stratification. Maximum total nitrogen was at least 0.5 milligram per liter during both years of the study, and maximum total phosphorus exceeded 0.05 milligram per liter during both years. Phytoplankton biovolume and chlorophyll a concentration were variable throughout the open-water season. The maximum chlorophyll a concentration was 6.1 micrograms per liter. Estimated nutrient loads for October 1989 through September 1990 were 13,400 kilograms of nitrogen and 1,490 kilograms of phosphorus from surface-water inflows and 13,300 kilograms of nitrogen and 687 kilograms of phosphorus from the bottom sediment. Most of the flux from the bottom sediment occurred during stratification. Most of the nitrogen loading from all sources and the phosphorus loading from the bottom sediment was in a dissolved form that is readily available for algal uptake. However, only about 20 percent of the phosphorus in the inflow water was in the available form of orthophosphate. A series of nutrient-limitation experiments was done to evaluate the algal response to phosphorus and nitrogen additions. Algal response was measured by changes in chlorophyll a concentration and phytoplankton biovolume. In every experiment, addition of both nitrogen and phosphorus was required to substantially increase algal biomass. No taste and odor problems developed in Standley Lake during the study period, and no organic compounds that create earthy or musty odors, such as geosmin or 2-methylisoborneol (MIB), were detected in any water samples from the lake, the inflows, or the outflow. Algae cultured from these water samples failed to produce earthy or musty odors. Few actinomycetes bacteria were detected in water samples, and none were recovered from Standley Lake bottom-sediment samples. INTRODUCTION Standley Lake is a reservoir that provides domestic water to the suburban cities of Northglenn, Thornton, and Westminster in Jefferson County, northwest of Denver, Colo. (fig. 1). In 1988, a taste and odor problem developed in water Although it is a reservoir, the word lake is used in its name. For consistency, it is referred to as a lake throughout this report.

Limnological characteristics, nutrient loading and limitation, and potential sources of taste and odor problems in Standley Lake, Colorado