This README file is associated with data and analyses from publication "Physical and biological constraints on the capacity for life-history expression of anadromous salmonids: an Eel River, California, case study" by FitzGerald et al. 2021, Canadian Journal of Fisheries and Aquatic Sciences. The shapefile is: EelRiver_data.shp. The .shp is GCS_NAD_1983, projected to GNLCC Albers, to be used in mapping software (e.g. ESRI ArcMap, QGIS). The .shp includes all stream segments in the Eel River watershed. Each stream segment has unique identifiers, an associated mean monthly air temperature (from 1993-2015), geomorphic channel type, predicted monthly wetted width, salmonid population potential use, and other stream segment characteristics. Fields are as follows: 'FID', 'Shape', 'OBSPRED_ID', 'COMID', and 'GNIS_NAME' are generic descriptors and identifiers. 'FTYPE' and 'WATERBODY' were not used in data analysis, but were used to eliminate reaches with unsuitable stream temperature predictions (e.g. lakes and reservoirs), when 'FTYPE' == "ArtificialPath" & 'WATERBODY' == 1. 'Month_Year' fields show the predicted mean monthly stream temperature from 1993-2015 for each stream segment (e.g. "Jan_93" indicates the mean temperature in January 1993). For our study, we examined temperatures in 2011 (cool year), 2015 (warm year), and 2002-2011 (averaged years), but here we include temperatures from each individual year from 1993-2015 for other research. For detailed methods on the stream temperature modeling or to obtain stream temperature predictions for 465,775 stream km in the western U.S. (i.e. including and beyond Eel River watershed), please refer to FitzGerald et al. 2021, Global Change Biology, https://doi.org/10.1111/gcb.15450 and FitzGerald et al. 2020, DRYAD dataset, https://doi.org/10.5061/dryad.n5tb2rbtq. 'length_m' is the length of each stream segment in meters. 'STL_access' and 'CHK_access' indicate if either steelhead (STL) or Chinook salmon (CHK) could potentially access that stream segment. A '1' means accessible; a '0' means inaccessible. Note that these fields do not necessarily imply presence. 'Pop_SW', 'Pop_SS', and 'Pop_CF' define each reach by salmonid subbasin. SW = winter-run steelhead, SS = summer-run steelhead, CF = fall-run Chinook salmon. Note that these fields do not necessarily imply presence or accessibility. A blank is outside of subbasin boundaries. 'ChanType' is our predicted geomorphic channel type from channel gradient and catchment area. 'BFwidth_m' is our predicted bankfull width in meters. 'width_Month' fields show our predicted wetted width in m for each stream segment for each month (average of years 2002-2015). 'ReachCateg' indicates the reach categorization for each stream segment based on channel gradient and upstream watershed area; reach categorization scale follows Cooper et al. 2020, Northwest Science.