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.
Tarryall Creek At Upper Station Near Como, Co
Withlacoochee River Near Cumpressco, Fl
Monatiquot River At East Braintree, Ma
Waller Ck At Red River St, Austin, Tx
Howell Creek Near Slavia, Fl
Mississippi River At Vicksburg, Ms
Perkiomen Creek At East Greenville, Pa
Clear Fk Trinity Rv Nr Weatherford, Tx
Barrel Canyon Near Sonoita, Az
Rio Chama Near La Puente, Nm
Elk Creek At Upper Station, Near Fraser, Co
Dowagiac River At State Hwy 51 Near Dowagiac, Mi
Contentnea Creek Nr Black Creek, Nc
Battle Creek Near Keystone,Sd
Canal 111 At S-18-C Near Florida City, Fl
Gwynns Falls At Villa Nova, Md
River Des Peres Near University City, Mo
Schoharie Creek Near North Blenheim Ny
Clear Fk Brazos Rv At Nugent, Tx
Walnut Creek Above Clanton, Ala
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.