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.
Flambeau River Near Bruce, Wi
La Crosse River At Sparta, Wi
Menominee River Below Pemene Creek Nr Pembine, Wi
Lemonweir River At New Lisbon, Wi
Milwaukee River Near Cedarburg, Wi
Sugar River Near Brodhead, Wi
Hay River At Wheeler, Wi
Oconto River Near Gillett, Wi
Black River Ds St Hwy 54 At Black River Falls, Wi
White River Near Ashland, Wi
Wisconsin River At Wisconsin Rapids, Wi
Platte River Near Rockville, Wi
Menominee River At Niagara, Wi
Crawfish River At Milford, Wi
La Crosse River @ Cnty Trunk Highwy Bb Nr Tomah,Wi
Badger Mill Creek At Verona, Wi
Black Earth Ck Nr Treatment Plnt @ Cross Plains,Wi
Swan Creek At Lalor Road Near Fitchburg, Wi
Black Earth Creek Nr Brewery Rd At Cross Plains,Wi
Green Lake At Green Lake, Wi
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.