Development of a Bio-assessment model for the Skagit watershed

The reference condition approach (RCA) was used to describe baseline water quality in streams of the 1,054 km2 Skagit River watershed north of the Canada/USA border. Reference condition describes a suite of biological and habitat attributes found at sites having little or no exposure to stressors caused by land use and other human activities. The premise behind the RCA is to sample a large number of sites in reference condition and use relationships between biological and environmental descriptors to build a predictive model that allows comparison of a test site with a reference condition. The Skagit model was called the Beast Assessment of Skagit Streams (BASS) in which “Beast” is an acronym for “Benthic Assessment of Sediment”, a type of RCA model that has been developed in Canada as a national bioassessment protocol. The bioassessment procedures are explained on the website called CABIN ( ). The project provided the Skagit Environmental Endowment Commission (SEEC) with an overview of present water quality in the Canadian portion of the Skagit watershed and a framework for monitoring potential development and natural changes to water quality in future years. BASS can show whether stream quality is changing over time and it can contribute to interpretations of effects of climate change or other regional environmental change that may affect water quality (e.g. fire or insect infestation). In these ways, bioassessment using BASS is a screening and learning tool that can feed into decisions to protect water quality.