We will follow the SLICES framework as a spatial context for fish community decadal assessments and site selection in the mainstem Willamette River(Hulse and Gregory 2004; http:ise.uoregon.edu/slices/Main.html).  The SLICES framework allows for a consistent spatial framework to track ecological conditions along the river and its floodplain while allowing the river channel to shift through time without altering the spatial context.  We will follow the fish and habitat surveys of the Willamette River Mainstem following protocol from initial decadal sampling from 2011-2013 (Williams et al. 2014).  We will stratify field sampling of the Mainstem Willamette River into three sections (upper, middle, and lower).  Each 1-km slice of the mainstem river or floodplain slough within a river slice represents a single sampling location.  Within each of the three Willamette River sections, there are various sentinal sites that will be sampled annually in addition to multiple randomly assigned sites that change annually.  Sentinal Slices are sampled annually.  We will sample native and non-native fish in the entire mainstem.  Sampling will be conducted from May 2021 to November of 2023.  Within each sample location, fish will be captured with a boat or backpack electrofisher by two netters.  We will sample shallow microhabitat types along the shore in each sampling site to represent the variety of nearshore habitats at each site.  At the end of each sampling effort, fish will be identified to species and measured ( length), and habitat characteristics measured.