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.
Buffalo Fork Ab Lava Creek, Nr Moran, Wy
Fish C Nr Ketchikan Ak
Tioga River Near Erwins Ny
Wekiva River Near Sanford, Fl
Strong River At D`Lo, Ms
Clear Fk Trinity Rv At Ft Worth, Tx
Puyallup River At Alderton, Wa
Weeki Wachee River Near Brooksville Fl
Licking River At Catawba, Ky
St. Joseph River At Three Rivers, Mi
Sf Coeur D Alene At Elizabeth Park Nr Kellogg Id
South River Near Ackworth, Ia
Allegheny River At Eldred, Pa
Yakima River At Mabton, Wa
Hatchie River At Bolivar, Tn
Tippecanoe River Below Oakdale Dam, In
Saco River Near Conway, Nh
Little Pigeon River At Sevierville, Tn
Sevier Riv Blw San Pitch Riv Nr Gunnison, Ut
Lowe R Ab Horsetail Falls Nr Valdez Ak
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.