US Water Quality Index
Our composite Water Quality Score combines temperature, reservoir levels, and flow rates to rate conditions for swimming, fishing, and recreation.
How We Calculate Water Quality Score (0–100)
Maximum points when water temp is near ideal 71.5°F (22°C) for most recreational activities.
Full points when reservoir is at or near full pool capacity. Low levels reduce score.
Moderate, stable flow (100–5,000 cfs) earns full points. Extreme highs or lows reduce score.
Vallecito Creek Near Bayfield, Co.
Taylor River Below Taylor Park Reservoir, Co.
South Platte River At Fort Lupton, Co.
Colorado River Below Baker Gulch Nr Grand Lake, Co
Yampa River Below Craig, Co.
Eagle River At Price Lane Bridge Near Gypsum, Co
Tomichi Creek At Gunnison, Co
Muddy Creek Above Antelope Creek Nr. Kremmling, Co
Yampa River Above Stagecoach Reservoir, Co
Monument Cr Abv Woodmen Rd At Colorado Springs, Co
Mcelmo Creek Above Trail Canyon Near Cortez, Co
South Platte River Abv Strontia Spgs Reservoir, Co
Saguache Creek Near Saguache, Co
Jimmy Camp Creek At Fountain, Co.
Arkansas River At Las Animas, Co.
Troublesome Creek Near Troublesome, Co.
Cimarron River Blw Cimarron Creek At Cimarron, Co
Fountain Creek Abv Manitou Ave At Manitou Spgs, Co
Mud Creek At State Highway 32, Near Cortez, Co.
Fraser River Blw Crooked Cr At Tabernash Co
Understanding the Water Quality Index
The US Water Quality Index is a composite score designed to give anglers, swimmers, boaters, and outdoor enthusiasts a quick, at-a-glance assessment of water body conditions. Unlike traditional water quality indices that focus on chemical pollutants (which require laboratory analysis), our index uses real-time USGS sensor data to reflect physical conditions relevant to recreation.
Temperature Component (40 points)
Water temperature is the most important factor for recreational fishing, swimming, and wildlife activity. The ideal range for most activities — comfortable for swimming, optimal for bass and walleye fishing — is approximately 65–78°F (18–26°C). Our scoring peaks at 71.5°F and decreases proportionally as temperature moves away from this ideal.
Reservoir Level Component (30 points)
Reservoir levels (measured as a percentage of full pool) reflect drought conditions, drought recovery, flood risk, and overall ecosystem health. A reservoir at full pool (100%) scores maximum points. Severely depleted reservoirs — common during drought — score fewer points. This metric is particularly relevant in western states where water storage is critical.
Flow Rate Component (30 points)
River discharge (measured in cubic feet per second, cfs) indicates safe boating, wading, and kayaking conditions. Moderate, stable flow rates between 100–5,000 cfs are typically ideal for most recreation. Extremely high flows indicate flood risk, while extremely low flows suggest drought stress and limited habitat for fish.