Starry stonewort (Nitellopsis obtusa)
https://www.dnr.state.mn.us/invasives/aquaticplants/starrystonewort/index.html
Species observations (current map)

Starry stonewort. Photo: University of Minnesota (https://maisrc.umn.edu/starry-stonewort)

A starry stonewort bulbil, which has a star-shaped rhizoid, giving the plant its namesake. Photo: Jim Grazio, PA DEP 2015 (https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=1688)