The Water Quality Index (WQI) is a tool used to measure water quality in streams. The WQI is a number ranging from 1 to 100; a higher number indicates better water quality. To produce a WQI score, we monitor streams monthly for temperature, pH, fecal coliform bacteria, dissolved oxygen, total suspended sediment, turbidity, total phosphorus and total nitrogen.
These measurements are compared to water quality curves and standards provided by the Washington Department of Ecology. The curves are based in part on state standards to maintain beneficial uses of our waters like recreation, drinking water and aquatic life habitat. The resulting scores are then combined and results aggregated over time to produce a single yearly score for each sample station.