Macrophytes serve important roles in improving water quality, combating erosion, and nutrient cycling. Research on freshwater macrophytes largely focuses on those in lakes or larger water bodies with little flowing current, and there is little consensus on what factors determine aquatic macrophyte distributions. We surveyed macrophytes at nine sites in the Carmel River Watershed in Monterey County, CA, to determine what environmental predictors affect their distributions and diversity within rivers, as well as the conditions that support important species. At each site, 50-meter transects were set up on both banks, one meter out from shore, or in the middle of a stream if it was two meters wide or less. Macrophyte counts and total cover were recorded, as well as depth, velocity, substrate size, and stream flow conditions. Additional measurements of water quality and canopy cover were taken at the midpoint of each transect. Macrophytes were identified using field guides and the i-Naturalist app, a global biodiversity database. Across all sites, we identified 17 species, of which four are invasive species. With 1,230 observations across all sites, the invasive Water Speedwell (Veronica anagallis-aquatica) is the dominant species within the system, followed by the invasive Water Mint (Mentha aquatica), with 864 observations. On the other hand, five native species were determined to be rare, with five or fewer observations. To better understand how environmental conditions affect the diversity and distributions of ubiquitous (often invasive) and rare taxa, I will conduct correlation analyses and run generalized linear models. I also plan to run a random forest model to determine the most likely environment in which rare taxa may be found. Ultimately, this research will lead to a greater breadth of knowledge on aquatic plants and their distributions and can provide essential information for their conservation.