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.
N.F. Peachtree Creek, Buford Hwy, Near Atlanta, Ga
Mosquito Creek Bl Mosquito Ck Dam Nr Cortland Oh
Floyds Fork Near Pewee Valley, Ky
Little Tallapoosa R At Reavesville Rd Nr Bowdon,Ga
Walker Rv Nr Mouth At Walker Lake, Nv
Lost River Diversion Channel Nr Klamath River, Or
Hudson River At Albany Ny
Monongahela R At Lock & Dam 8, At Point Marion, Pa
Arkansas River Near Rocky Ford, Co.
Illinois River At Florence, Il
Yampa River Near Maybell, Co
Okanogan River At Malott, Wa
Snapfinger Cr At Thompson Mill Rd Nr Lithonia, Ga
Walker Rv Nr Wabuska, Nv
Turkey Creek At Sewage Plant Near Pinson Al
Hyco R Bl Abay D Nr Mcgehees Mill, Nc
Floyds Fork Near Mt Washington, Ky
Willamette River Below Falls, At Oregon City, Or
Aiw At Highway 544 At Socastee, Sc
Cooper R At Mobay Nr N Charleston, Sc
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.