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 Bed Nr Ririe Id
Snake River At Blackfoot Id
Nf Coeur D Alene River At Enaville Id
Fall River Nr Squirrel Id
Deadwood River Bl Deadwood Res Nr Lowman Id
Payette River Nr Letha Id
Portneuf R. Abv Toponce Rd, Nr Chesterfield, Id
Sf Salmon River Nr Krassel Ranger Station Id
Priest River Near Priest River, Id
Little Wood River Ab High Five Creek Nr Carey Id
Sf Coeur D Alene River Abv Pine Cr Nr Pinehurst Id
Nf Teton River Nr Sugar City Id
Spring Creek At Sheepskin Rd Nr Fort Hall Id
Boundary Creek Nr Porthill Id
Spokane River Blw Blackwell Nr Coeur D Alene Id
Willow Creek Blw Floodway Channel Nr Ucon Id
Snake River Nr Twin Falls Id
Nf Coeur D Alene R Ab Shoshone Ck Nr Prichard Id
Fall River Ab Yellowstone Canal Nr Squirrel Id
Sand Run Gulch Nr Parma Id
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.