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 Blw Lambert Br Nr Geyserville Ca
Firehole River At Old Faithful, Ynp
Taylor River At Taylor Park, Co.
Savage Riv Bl Savage Riv Dam Near Bloomington, Md
Upper Clear Creek Near Kooskia, Id
Cedar River At San Juan Avenue At Jacksonville, Fl
Crystal River Near Crystal River Fl
Pohopoco Cr Bl Beltzville Dam Nr Parryville, Pa
Miller Creek Near Beaver Marsh, Or
Hills Cr Ab Hills Cr Res, Nr Oakridge, Or
Bonnet Creek Near Vineland, Fl
Coast Fork Willamette R Blw Cottage Grove Dam, Or
Glenbrook Ck At Glenbrook, Nv
Middle Santiam River Nr Santiam Junction, Or
Sf Tolt River Bl Regulating Basin Nr Carnation, Wa
Blacktail Creek Above Grove Gulch, At Butte, Mt
Pequannock River At Oak Ridge Nj
Black Lk Outlet At S-101A, At Lake Buena Vista, Fl
Bull Run River Near Multnomah Falls, Or
Grand Portage River At Grand Portage Mn
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.