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.
Delaney Creek Near Tampa Fl
Wickahoney Creek Nr Grasmere, Id
Ramapo River At Suffern Ny
Deepwater Creek At Mouth Nr Raub, Nd
L Medicine Bow R At Boles Spring, Nr Medicine Bow
Coginchaug River At Middlefield, Ct
Powder Springs Creek Near Powder Springs, Ga
Slate River Near Arvonia, Va
Pigeon Creek Nr Angola, In
South Fork Licking River Near Hebron Oh
Banning Creek Near Bisbee, Az
Kings Cyn Ck Nr Carson City, Nv
Fourmile Canyon Creek Near Sunshine, Co
Econfina River Near Perry, Fla.
Hanapepe Riv Blw Manuahi Str Nr Eleele, Kauai, Hi
Cohansey River At Seeley Nj
Canyon Creek Near Cedar Falls, Wa
Calumet Union Drainage Canal Near Markham, Il
Marrowbone Ck At Mud Camp Rd At Waterview, Ky
Wb Wapsinonoc Cr At College St At West Branch, Ia
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.