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.
Aravaipa Creek Near Mammoth, Az.
Rillito Creek At Dodge Boulevard, At Tucson, Az
Chevelon Creek Near Winslow, Az
Levee Canal Wasteway Near Yuma, Az
Cherry Creek Near Globe, Az
Trout Creek Above Knight Creek, Near Wikieup, Az
Las Moras Wash (Lower Station) Near Sasabe, Az
Sycamore Creek Above Verde Rvr, Near Clarkdale, Az
Eagle Creek Above Pumping Plant, Near Morenci, Az.
Agua Fria River Near Rock Springs, Az
Santa Cruz River Near Nogales, Az.
Gila Monster Farms Turnout No. 1 Near Yuma, Az
Altar Wash Near Three Points, Az.
Little Colorado River Near Cameron, Az
South Gila Terminal Canal Wasteway Nr Yuma, Az
Pinto Creek Near Miami, Az
Santa Maria River Near Bagdad, Az
Verde River Above Camp Verde, Az
Gila River Below Coolidge Dam, Az.
Hassayampa River Near Arlington, 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.