The lower Yakima River (LYR) is a bottleneck for Pacific salmon migrating to their spawning grounds. Daytime temperatures are often too high, while nighttime dissolved oxygen (DO) concentrations are often too low. The likely culprit for the low nighttime DO is respiration by water stargrass (Heteranthera dubia). Water stargrass (WSG) is native to the LYR, but changing precipitation regimes (i.e., smaller snowpack leading to an earlier, smaller spring freshet) have expanded its reach to the entire river width. One potential management strategy is to remove WSG with a commercial harvester, thereby decreasing biomass and total respiration and increasing nighttime DO concentrations. Before undertaking harvest on a large scale, we propose to test its effects on two smaller patches. We will do sowith a Before-After-Control-Impact experimental design. At each plot, we will deploy DO and temperature sensors, characterize the benthic substrate and flow, and measure respiration in each compartment (WSG, benthic sediments, and the water column). With these measurements, we will assess the effect of WSG harvest on the direct limitations to salmon migration and spawning (DO, temperature, habitat) and the mechanisms behind those limitations (respiration, flow). Fundamentally, this project will contribute to our understanding of macrophyte effects on ecosystem function, a topic that has been mostly ignored in rivers. More immediately, this pilot project will inform management efforts in the LYR and elsewhere ,while solidifying and fostering WSU-agency partnerships.