Observation for Ceratophyllum demersum: https://www.inaturalist.org/observations/223230727
Found these at the North end of Long Pond in Grafton Lakes State Park (Rensselaer County, NY). At first glance I thought it was spineless hornwort because of those cupped whorls, but upon closer inspection the leaves have a milfoil structure--Feather-divided, 6 pairs of leaflets on each of 4 leaves on the cross section in picture 2. The plant is very fragile, so it is possible I damaged it while breaking off pieces. Is this Myriophyllum alterniflorum?