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.
E Fk Little Miami River Bl Harsha Dam Nr Bantam Oh
Swatara Creek At Middletown, Pa
Rock River At Latham Park, Il
Missouri River At Fort Benton Mt
Pilot Creek At County Hwy P15 Near Rolfe, Ia
S F Flathead R Ab Twin C Nr Hungry Horse Mt
Meramec River At Fenton, Mo
Clear Ck At Ft Hood, Tx
Chattahoochee River Buford Dam Nr Buford, Ga
Bushley Bayou Nr Harrisonburg, La
North Blackbird Creek At Hwy 75 At Macy, Nebr.
Palatlakaha River Below Spwy, Near Mascotte, Fl
Stockton Lake Near Stockton, Mo
Grizzly Bear Creek Near Keystone,Sd
Sabinal Rv At Utopia, Tx
Lugert Drainage Ditch At Lugert, Ok
Cahaba River Near Trussville, Ala
Missouri River At Washburn, Nd
Bayou Teche Below Keystone L&D Nr St. Martinville
Cow Bayou At Ih 10 Nr Vidor, Tx
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.