What you have is definitely hydrilla, probably hydrilla verticillata. If you look at the chart I posted you will see that the leaf whorls are in groups of five, which is what you have. Anacharis is from the egeria family and has more leaves per whorl and the leaf margins are smooth. Hydrilla is an extremely invasive non native and is choking out local waterways all across the USA. I believe it is also on the federal ban list.