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.
Cottonwood Creek At Woodmen Rd Nr Colo Springs, Co
Turkey Cr West Seep Bl Teller Res Nr Stone City,Co
Elliott Creek Feeder Canal To Green Mtn Res, Co
Rock Creek Above Fort Carson Reservation, Co
Lena Gulch At Lakewood, Co
Big Dry Creek At Mouth Near Fort Lupton, Co
Dolores River Near Slick Rock, Co
Grizzly Creek Nr Grizzly Lake Nr Glenwood Spgs, Co
South Platte River At Fort Morgan, Co
Canyon Creek Near New Castle, Co.
Williams Canyon Abv Mouth Near Manitou Springs, Co
Plum Creek Near Sedalia, Co.
Cascade Cr Blw Cascade Cr Diversion Nr Rockwood Co
Ohio Creek Above Mouth Nr Gunnison, Co
Bear Creek Near Colorado Springs, Co
Lakewood Gulch At Denver, Co
St. Charles River At Vineland, Co.
Castle Creek Above Queens Gulch Near Aspen, Co
Roaring Fork River Near Aspen, Co.
Trail Creek Near 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.