The Blue River drains approximately 680 square miles west of the Continental Divide in central Colorado before flowing northward into the Colorado River near Kremmling, Colorado. The Blue River watershed (BRW) is almost entirely located in Summit County and includes the towns of Breckenridge, Dillon, Frisco, Montezuma, and Silverthorne. Dillon Reservoir and Green Mountain Reservoir are major water storage facilities in the watershed. The BRW upstream from Dillon Reservoir is in the Colorado Mineral Belt, a zone of economically significant metals deposits. Hard-rock mining was the major industry in this area from 1859 through the first half of the 1900s. With the development of ski areas beginning in 1945 and the construction of Interstate-70, Summit County has become a major four-season resort destination. Ski resorts such as Arapahoe Basin, Breckenridge, Copper Mountain, and Keystone have brought rapid population growth and increased tourism and development to the area.
Mineralized bedrock, historical mining activities, and more recent urban development related to population growth, tourism, second-home development, and recreation have affected water quality and aquatic biota in the BRW. High concentrations of trace elements can occur naturally from the weathering on mineralized rock and acid mine drainage. Septic and wastewater systems and runoff from developed lands can affect nutrient concentrations in water bodies, and highway sanding in winter can increase sediment loading to nearby streams. With these considerations, the USGS, in cooperation with the Summit Water Quality Committee, is conducting a study to compile and assess water quality in the BLW. Specific objectives of the study are to: