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.
Little Pee Dee R. At Galivants Ferry, Sc
Buffalo River Near Flat Woods, Tn
Tongue River At State Line Nr Decker Mt
Colorado R. Abv Gunnison R. At Grand Junction, Co
Kankakee River At Dunns Bridge, In
Kawishiwi River Near Ely, Mn
Jackson River At Falling Spring, Va
Appomattox River At Matoaca, Va
Greenbrier River At Alderson, Wv
Bluestone River Near Pipestem, Wv
French Broad River At Asheville, Nc
Clinton River At Moravian Drive At Mt. Clemens, Mi
Etowah River At Ga 9, Near Dawsonville, Ga
Cuyahoga River At Jaite Oh
Sf Coquille River At Myrtle Point, Or
North Umpqua River At Winchester, Or
Delaware R Above Lackawaxen R Near Barryville Ny
Scioto River Near Prospect Oh
Arkansas River Below John Martin Reservoir, Co.
Erie (Barge) C Abv Halls Waste Weir At Lockport Ny
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.