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.
Mohawk River At Rexford Ny
North Boggy Creek At Garriott Rd At Enid, Ok
Bear Lake At State Park Marina Nr Garden City, Ut
Site 19 In Conservation Area 2A Nr Coral Springs
Neosho River Near Commerce, Ok
Tensas River Se Of Tendal, La.
Nuyakuk R Nr Dillingham Ak
West Branch Rahway River At Millburn Nj
Lake Michigan At Chicago Lock At Chicago, Il
Pontoon Bridge Canal Near Butte Larose, La
Greenwood Reservoir Near Greenwood, Mi
10B Reedy Creek Below S-46 Nr Vineland Fla
Cypress Ck At Sharp Rd Nr Hockley, Tx
Tank Creek At Longstreet Road At Fort Bragg, Nc
Beaver Creek Nr Hulen, Ok
Big Papillion Creek Near Blair, Nebr.
Clearwater Tailwater Near Piedmont, Mo
Little Calumet River At Burr Street At Gary, In
Vermilion River (B. Vermilion) Near Carencro, La
Coosa River At Gadsden Al
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.