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.
Spring Creek Near Mason City, Ia
Site 76 In Conservation Area 3B Nr Andytown, Fl
Watson Creek Trib 2, Tanglewood Dr, Snellville, Ga
Ramapo River At Dawes Highway At Pompton Nj
Beckwith Ck East Of Dequincy, La
Pepacton Res Div Outlet Nr Grahamsville Ny
Goose Ck Nr Mcnair, Tx
Sand Creek Below Little Rock Creek Near Okesa, Ok
Hurricane Creek Near Humphrey, Ar
Missouri River At Niobrara, Nebr.
Ubc Dam 101 At O'Connor Blvd Nr Round Rock, Tx
Red River At Yawn Estate Near Cash Point, La
Bayou Macon At Hwy 134 East Of Epps, La
Cherry Valley Run At Leetonia Oh
Prompton Reservoir At Prompton, Pa
Sb Raritan R At Black Point Rd At Neshanic Sta Nj
Fox Lake Near Lake Villa, Il
Little River Blw Lukfata Creek, Nr Idabel, Ok
Kennebec River At Calumet Bridge At Augusta, Maine
Austin Lake Near Kalamazoo, Mi
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.