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.
Dry C Nr Galt Ca
Salt River Near Roosevelt, Az
Jemez River Outlet Below Jemez Canyon Dam, Nm
Williams Fork Below Williams Fork Reservoir, Co
Fondulac Creek Near East Peoria, Il
Portage Creek At Kalamazoo, Mi
Belle Fourche River At Wy-Sd State Line
Barrilla Draw Nr Saragosa, Tx
Saddle Creek At Structure P-11 Near Bartow Fl
Willow Creek Bl Tex Creek Nr Ririe Id
Sf Republican R Nr Co-Ks St Line, Ks
Myrtle Brook At State Hwy 214 At Edgewood Ny
Boggy Creek At 30Th St At Enid, Ok
Big Quilcene River Below Diversion Nr Quilcene, Wa
Eagle Valley Ck At Carson City, Nv
Amargosa Rv At Tecopa, Ca
Driftwood Creek Near Mccook, Nebr.
Cedar Creek Nr Haynes, Nd
Dry Creek Near Edenwold, Tn
Upper Nuka R Nr Park Boundary Nr Homer Ak
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.