Glisson, Wesley JLarkin, Daniel J2021-11-152021-11-152021-11-15https://hdl.handle.net/11299/225295The files include data collected at each Myriophyllum sampling location over the course of the study, including data collected at the water's surface (Myriophyllum flower heads, Myriophyllum surface cover, and water chemistry) and data collected with the underwater video sampling device (Myriophyllum stem counts and vertical stem cover). Surface data include a single row for each site (i.e., point location) on each lake for each sampling event. The underwater stem data includes multiple rows for for each site on each lake for each sampling event; these rows correspond to four video subsamples collected at each site, and subsequent 0.5-m depth intervals at which Myriophyllum stems were assessed for each subsample. Additionally, there is a data file that includes biomass measurements that correspond to stem counts from video subsamples. Data across files can be linked via "siteID".In North America, the hybrid aquatic plant Myriophyllum spicatum × Myriophyllum sibiricum (hybrid watermilfoil, HWM) is a cross between non-native invasive Eurasian watermilfoil (M. spicatum, EWM) and native northern watermilfoil (M. sibiricum, NWM). We compared HWM to its parental taxa, EWM and NWM, by examining the amount and timing of: 1) flowering, 2) surface cover, and 3) biomass (using stem counts as a proxy). We conducted repeat surveys of Myriophyllum beds at eight lakes (2–3 lakes/taxon) in the Minneapolis-St. Paul Metropolitan area (Minnesota, USA) between June 2017 and November 2018. To sample biomass without destroying plants, we developed a novel sampling device that uses underwater video to measure Myriophyllum stems; we validated the utility of this device by comparing Myriophyllum stem counts and biomass collected from the same locations. The data from these studies are provided and documented here.Attribution-ShareAlike 3.0 United StatesAquatic invasive speciesFreshwater ecosystemsHybrid vigorInvasive traitsMacrophytesNon-destructive samplingPhenologyDatasethttps://doi.org/10.13020/5xq3-wb66