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.
Flint Creek At Maxville Mt
Old Catawba R Bl Catawba Dam Near Bridgewater, Nc
Bear Butte Creek Near Deadwood, Sd
Tenaha Ck Nr Shelbyville, Tx
Brewery Creek-Upstream Site-At Cross Plains, Wi
South Fork Chariton River Near Promise City, Ia
Hollow Tree Brook At Lanesville Ny
Pete Hanson Ck Abv Henderson Ck Nr Eureka, Nv
Ebenezer Creek At Springfield, Ga
Gamble Creek Near Parrish Fl
Big Lost River Ab Big Lost River Sinks Nr Howe Id
Republican River Near Orleans, Nebr.
Porcupine Creek Near Fort Yates, Nd
Harpeth River At Franklin, Tn
Ephraim Tunnel Near Ephraim, Ut
Cuyama R Nr New Cuyama Ca
Sewell Mill Creek At Ga 120, Near Marietta, Ga
Chester C At Arctic Boulevard At Anchorage Ak
St. Joseph R At Parnell Av At Fort Wayne, In
Yalobusha River At Grenada, Ms
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.