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.
Big Thompson River At Loveland, Co.
Vasquez Creek At Winter Park, Co
Turkey Creek Ab Teller Res Near Stone City, Co.
Tarryall Creek At Upper Station Near Como, Co
Texas Creek At Taylor Park, Co
Little Dry Creek Nr Arapahoe Rd At Centennial, Co
Mcelmo Creek Near Colorado-Utah State Line
Cimarron River Near Cimarron, Co
Lytle Ditch At Ft. Carson, Co
Hubbard Creek At Highway 133 At Mouth Nr Bowie, Co
Piney River Below Piney Lake, Near Minturn, Co.
Fountain Creek At 8Th Street At Pueblo, Co
Big Dry Creek At Westminster, Co
Lake Creek Near Edwards, Co
Arkansas River At Holly, Co.
Arkansas River Tributary Above Hwy 227 At Pueblo
West Plum Creek At Sedalia, Co
Coal Creek Abv Mccormick Dtch At Crested Butte, Co
Dry Gulch At Denver, Co
Sand Crk Abv Burlington Ditch Nr Commerce City, 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.