The effects of the highway deicing activities on the Peshastin Creek watershed were studied over a 6-month period from December 1999 to May 2000. Three threatened and/or endangered species, steelhead (Oncorhynchus tshawytscha), Chinook salmon (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus), inhabit the stream and, therefore, a study of the effects of deicing activities was warranted. Five reaches along Peshastin Creek and its tributaries were selected for the collection of weekly grab samples and three of these reaches were outfitted with continuous monitoring equipment. Water quality tests, Microtox (registered trademark) toxicity tests, benthic macro invertebrate enumeration and streambed substrate sieve analyses were used to evaluate the influence of deicing activities (application of traction sand and IceBAN, a liquid deicer) on Peshastin Creek. Chloride exhibited signs of preferential elution and was also found to be significantly higher in concentration in areas adjacent to the US Highway 97. The maximum recorded chloride concentration in Peshastin Creek was 3.3 and 2.7 mg/L at Reach 2 and Reach 4, respectively. The non-impacted reaches of Peshastin yielded an average chloride concentration of 0.62 mg/L. Heavy metal concentrations (soluble and total) were much lower than the US EPA recommended limits. The benthic macro invertebrate study, although qualitative in nature, suggested that the deicing activities did not adversely impact the three fish food organisms that were quantified. Streambed substrate analyses indicated that the traction sand used in deicing activities had no measurable negative impact on known spawning locations. The physical, chemical, and biological parameters evaluated in this study indicate that deicing activities along SR 97 had no measurable negative impact on Peshastin Creek.