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The Spokane Riverkeeper partnered with Spokane Falls Trout Unlimited and local community scientists for the fifth year to measure and determine the effect of Hangman Creek’s annual sediment plume on water clarity (turbidity) in the Spokane River. Turbidity is the measure of light refraction in the water and measured in nephelometric turbidity units (NTU). Total suspended solids (TSS) are the physical particles in the water column which create turbidity (“Turbidity and Water” 2001). Turbidity is also one of many ways used to measure water pollution in Washington. From December 2021 to June 2022, 21 community scientists performed 95 sampling events and collected 310 water samples from the Spokane River and Hangman Creek. These samples were analyzed for turbidity and compared against state standards. The reason for this study was to determine the effects (if any) on the Spokane River (primary Interest) from the polluted (turbid) water flowing in from Hangman creek. The results showed that 18 turbidity violations occurred over the course of the study in the Spokane River due to Hangman Creek. This means that Hangman Creek caused the Spokane River to exceed Washington State Water Quality Standards (WQS) 26% of the time (Table 1).
The turbid water is polluting the Spokane River to such a degree that fish habitat and other important qualities are degraded. Washington Department of Ecology (2006)states, high levels of turbidity cause fish and benthic macroinvertebrates to have reduced growth rates, reduced disease resistance, less successful or reduction of egg laying/rearing, modified migration, altered predator/prey relationships, and reduced ability to feed. Turbidity allows transmission of bacterial or viral particles that attach themselves to suspended particles in the water, which interferes with human health