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.
Muddy River Near East Wallingford, Ct
Bull Mountain Creek At Tremont, Ms
Tuscarawas River Above Barberton Oh
N Fk Red Rv Nr Shamrock, Tx
Chevelon Fork Below Wildcat Canyon, Nr Winslow, Az
Tonkin Spg Outflow Abv Denay Ck Nr Eureka, Nv
Mc Donald Creek Near Mount Prospect, Il
Skaneateles Creek Near Skaneateles Junction Ny
Peach Ck Bl Dilworth, Tx
Whitewater R A Rancho Mirage Ca
Heeia Stream At Haiku Valley Nr Kaneohe, Oahu, Hi
Bear Br At Research Blvd, The Woodlands, Tx
Little R Nr Trinidad Ca
East Fork Shoal Creek Near Coffeen, Il
West Fork Drakes Creek Near Franklin, Ky
South Omaha Creek At Walthill, Nebr.
San Marcos Spgs At San Marcos, Tx
Bear Creek At Friendsville, Md
Little River Blw Lk Thunderbird Nr Norman, Ok
Salmon Creek Above Diversion Near Okanogan, Wa
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.