This dataset provides information collected at three stream monitoring sites on the lower Yakima River in Washington State from June 2018 through September 2020 by the U.S. Geological Survey. Sample locations included the Yakima River at Prosser, WA (USGS Station, 12509489), the Yakima River at Kiona, WA (USGS Station, 12510500), and the Yakima River at Van Giesen bridge near Richland, WA (USGS Station, 12511800). Water stargrass (Heteranthera dubia) biomass was collected six times from August 2018 to August 2020 from all three sites. Plant samples were dried and areal mass was measured in grams per square meter squared (g/m2). These data are provided in the files “Yakima.biomass.csv”. The presence/absence of water stargrass surrounding each monitoring station was determined by counting if water stargrass was present at 1-meter intervals along 5 to 10 transects at each monitoring station; these counts are provided in the file "Yakima.biomass.point.counts.csv". In addition, stream metabolism was modeled at two sites: the Yakima River at Kiona, WA from June 2018 to October 2020, and Yakima River and at Van Giesen bridge near Richland, WA from August 2018 to March 2020 using the streamMetabolizer package in R. For each site, four files are provided; (1) the input data, which includes continuous dissolved oxygen, solar time, water temperature, light, and stream depth, (2) the output file containing the daily metabolism estimates, (3) a site-specific html 'guide' for running the streamMetabolizer package in R, and (4) a README text file explaining file contents. Model input data were downloaded directly from the USGS National Water Information System (NWIS) (dissolved oxygen and temperature), downloaded directly from data loggers deployed in the field (light and depth), or calculated in the StreamMetabolizer program (DO saturation and solar time). Finally, water quality control data from discrete nutrient sampling are provided. These data include results from 6 field blanks (blanks.csv) and 6 sets of field replicates (replicates.csv) collected during this study. Refer to "version_notes.txt" for specific updates to version 2.0 of this data release. First release: 2024-07-29 (ver. 1.0) Revised: 2025-08-13 (ver. 2.0)