Physical, chemical, and biological water quality data were collected and compiled for five sites in Arvada Reservoir, one site in Ralston Creek, and two sites in Croke Canal, in the Denver metropolitan area, Colorado. The purpose of the data collection was to determine the water quality of Arvada Reservoir, evaluate the effect of source waters on the reservoir , and determine the trophic state of the reservoir. Data collected include reservoir profile measurements with depth and inflow measurements of water temperature, specific conductance, dissolved oxygen, and pH. Secchi disk depth measurements also are reported. In addition, water samples were analyzed periodically for concentrations of major chemical constituents, nutrients, trace elements, and selected radiochemicals; for densities and relative abundance of phytoplankton and zooplankton; and for concentrations of chlorophyll alpha. Results of algal growth potential determinations are included. This report describes sampling site locations and methods of data collection and analyses and presents qualitative and quantitative results of water quality data collected during the study. Sampling began during June 1983 and continued through September 1985. (USGS)