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.
North Oak Creek At Valparaiso, Nebr.
Little Missouri River Above Mouth Near Oakdale, Nd
Fourmile Draw Nr Lakewood, Nm
Hackensack River At Rivervale Nj
Tohickon Creek Near Pipersville, Pa
Steamboat Ck At Steamboat, Nv
Rock Creek Above Fort Carson Reservation, Co
L-67C Canal Ups Of S-152 Flowway Nr Coopertown,Fl
Big Muddy Creek Nr Mouth Nr Culbertson Mt
Green Lake Sw Inlet @ Ct Highwy K Nr Green Lake,Wi
Aspen C Abv Leviathan Mine Nr Markleeville Ca
Cypress Slough Near Basinger, Fl
Hakalau Stream Nr Alt 1300 Ft, Hi
James Run Near Belcamp, Md
Glens Falls Feeder At Dunham Basin Ny
Mill Creek At Garfield Hts Oh
Tuscarora Creek Near Port Royal, Pa
Hunting Bayou At Ih 610, Houston, Tx
Chamokane Creek Below Falls Near Long Lake, Wa
Las Moras Wash (Middle Station) Near Sasabe, Az
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.