Re: fresh water jellyfish pic
 

Is there such a thing as a freshwater jellyfish?

Yes, but... the freshwater "jellyfish" as you are referring is not a true jellyfish as are some of its marine relatives. Freshwater "jellyfish" differ slightly from the true marine jellyfish. Craspedacusta sowerbii is the scientific name of this freshwater "jellyfish".

One obvious difference is that unlike marine jellyfish, C. sowerbii has a structure called a velum on the ventral surface. This thin, shelf-like membranous structure extends inward from the circular edge (ring canal) of the bell. The manubrium, which ends in a mouth, extends down through a hole in the velum. The velum helps set C. sowerbii apart from the true jellyfish. However, because C. sowerbii looks like a jellyfish, we call it a jellyfish!

C. sowerbii belongs to the class Hydrozoa which includes the more common hydra.

Re: fresh water jellyfish pic
 

There's a pond in orange county just south of West point that is also known for these.