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.
West Brook At Austin Lincoln Park At Walton Ny
North Canadian River Near El Reno, Ok
Brandy Run Near Girard, Pa
Brazos Rv At Richmond, Tx
Mill Cr At Last Chance Rd Br Nr College Place, Wa
Santa Fe River Above Cochiti Lake, Nm
Farm River At Totoket Road At Totoket, Ct
Mountain Creek Near Glendale, Tn
Blackwater River At Route 620 Near Zuni, Va
Boulder Creek At North 75Th St. Near Boulder, Co
Frontier Ditch Return Nr Coolidge, Ks
East Branch Swift River Near Hardwick, Ma
Guadalupe Rv Nr Center Point, Tx
Brock Reservoir Inlet Near Calexico, Ca
Halaulani Str At Alt 400 Ft Nr Kilauea, Kauai, Hi
Brush Creek At Ward Parkway In Kansas City, Mo
Novato C A Novato Ca
Duchesne River Near Hanna, Ut
Spirit Creek At Us 1, Near Augusta, Ga
Twin Creek At Eight Mile Road Near Evart, Mi
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.