Cabomba caroliniana is its official name.
Pete found a good picture of it.
I found some washed up on the shores of our big river
here. Looking at the USDA distribution map, our county
seems to be one of two in our state that has it. Considered
a Class B noxious weed.... rats!
Next time we get in the pond I'll have the guys pull it out.
It can't really get anywhere from our pond, we are not
on a flood plain, but I did have two ducks in there the other
day and they could transfer broken parts - all sorts of
things can be transferred from pond to pond via birdy feet.

One year I brought home purple loosestrife from the same
river, also making unwanted in rounds in our rivers and
wetlands. I kept in a protected place, grew it for a while,
saw who tough it was and then dried it out before it made
any seeds. It stayed in a dry spot and went thru a rotten
winter and darned if it didn't come back to life. Franken
Plant!! This time made sure it wouldn't come back to life.

k :-)