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.
St. Joseph Creek At Route 34 At Lisle, Il
Cedar River At County Road 366 Nr Cedar River, Mi
Loup Loup Creek At Malott, Wa
Long Quarter Branch At Lutherville, Md
Little Killbuck Creek Near Lodi Oh
Quittapahilla Creek Near Bellegrove, Pa
Homestake Creek At Gold Park, Co.
Rio Puerco Near Bernardo, Nm
Prairie Creek Upstream Of Sr 31 Near Ft Ogden Fl
Tongue River At Akra, Nd
Cow Creek Abv Galesville Res, Nr Azalea, Or.
Spring Creek Below Lebanon, Tn
Maggie Ck Abv Maggie Ck Cyn Nr Carlin, Nv
Slide Ditch Flume Blw Hwy 135 Nr Crested Butte, Co
Falls C Nr White Water Ca
Spring Creek Near Leary, Ga
Big Cypress Bayou Nr Jefferson, Tx
South Platte River Below Union Ave, At Englewood,C
White R Bl Tabbyune Crk Nr Soldier Summit, Ut
Big Creek Near Clermont, Fl
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.