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 Creek Above Antelope Creek Nr. Kremmling, Co
Clover Ditch Drain At Quinn St Nr Widefield, Co
Black Sulphur Creek Nr Wet Swizer Cr Nr Rangely Co
Loutsenhizer Arroyo At Hwy 50 Near Olathe Co
Bessemer Ditch At St. Charles Wd Near Pueblo Co
Yampa River At Steamboat Springs, Co
Arkansas River At Las Animas, Co.
Saguache Creek Near Saguache, Co
Green River Above Gates Of Lodore, Co
Mcelmo Creek Above Trail Canyon Near Cortez, Co
Yampa River Above Stagecoach Reservoir, Co
Black Sulphur Creek Blw Canyon Creek Nr Rangely Co
Yampa River At Deerlodge Park, Co
Ranch Creek Blw Meadow Cr Nr Tabernash, Co
Mud Creek At State Highway 32, Near Cortez, Co.
Troublesome Creek Near Troublesome, Co.
Yampa River Near Maybell, Co
Anthracite Creek Above Mouth Near Somerset
Fountain Creek Abv Manitou Ave At Manitou Spgs, Co
Taylor River At Almont, Co.
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.