Water quality of the Medicine Bow River Basin

The state of Wyoming is required to monitor the chemical, physical, and biological integrity of freshwater resources under the Clean Water Act (CWA). However, the paucity of background water quality data is inhibiting accurate designations of waterbody classifications, beneficial uses, and water quality impairments. The primary objective of this paper was to collect credible baseline data, following standards mandated by the Wyoming state legislature to facilitate Wyoming's efforts to meet intentions of the CWA. Specific objectives were to identify background and degraded water quality conditions, and provide a case study for the effectiveness of Wyoming's index of biological integrity (IBI) for identifying impaired or degraded stream reaches.;Chemical, physical, and biological data were collected for nine sites on three streams to test the effectiveness of Wyoming's index of biological integrity in mountain and semi-arid landscapes. The Beneficial Use Reconnaissance Project (BURP) followed our a priori expectations by responding to physical parameters as apposed to water column chemistry. The IBI responded with relative predictability to environmental gradients of substrate, velocity, suspended solids, and habitat conditions. These causal relationships demonstrate the capacity of Wyoming's IBI to identify impairments or accelerated rates of change in physical parameters. Results and analysis stress the importance of collecting supplemental data on physical and chemical parameters at potentially impaired sites, to help determine what restoration efforts are needed, if any.;Water quality of the Medicine Bow River Drainage is strongly influenced by the weathering and dissolution of geologic parent material, which intensifies along longitudinal gradients from headwaters to basin outlets. Dissolved and suspended solids varied among rivers, elevation zones, and sampling years. Except for basin temperatures and stream discharge, observed water quality gradients appear to represent background conditions for this geographic location.