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.
Saluda River Near Williamston, Sc
Cooper River At U.S. Hwy 17 At Charleston, Sc
Saluda River Near Columbia, Sc
South Saluda River Near Cleveland, Sc
Eastatoee Crk On Cleo Chapman Hwy Near Sunset, Sc
North Saluda River Above Slater, Sc
Broad River Near Carlisle, Sc
Catawba River Bl Lake Wylie Dam Fewell Island, Sc
Little Pee Dee R. At Galivants Ferry, Sc
Saluda River Below Lk Murray Dam Nr Columbia, Sc
Wateree River Nr. Camden, Sc
Broad River Near Columbia, Sc
Aiw At Myrtlewood Golf Course At Myrtle Beach, Sc
Aiw At Highway 9 At Nixons Crossroads, Sc
Santee River Near Pineville, Sc
Santee River Near Russellville, Sc
Catawba River At Great Falls, Sc
Great Falls Reservoir Tailrace Bl Great Falls, Sc
Rediv Canal At Santee River Nr St Stephen, Sc
Mctier Creek Rd 209 Near Monetta, Sc
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.