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.
Colorado River Below Baker Gulch Nr Grand Lake, Co
Jackson Creek Near Lenz, Or
Smith River Abv Trail Brdg Resv Nr Belknap Springs
Pilgrim River At Paradise Rd Nr Dodgeville, Mi
North Fork Tolt River Near Carnation, Wa
Salmon Trout River Near Big Bay, Mi
Flathead River At Columbia Falls Mt
Fir Creek Near Brightwood, Or
St. Louis Creek Near Fraser, Co.
Blue River Near Dillon, Co
Sand Creek Blw Sand Creek Canal Nr Chinchalo, Or
Big Warm Spgs Nr Duckwater, Nv
Bull Run River Blw Bull Run Res 2, Nr Bull Run, Or
Colorado River Near Granby, Co
South Fork Tolt River Near Index, Wa
East Branch Salmon Trout River Near Dodge City, Mi
Nf Tolt River Above Yellow Creek Nr Carnation, Wa
Ranch Creek Near Fraser, Co.
Washington Creek At Windigo, Mi
Pecos River Near Anton Chico, Nm
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.