I have never seen any in freshwater, wow. Is Neponsett connected by a tidal river? I never been there so I'm not sure. For the last week or so the salt water is loaded with all different kinds of jellies.
Yup. They can be appeared for no reasons. My pond has them like ten years ago. I told my parents about it. They said I was full of .... Lol then next night, I caught them and put into bucket to show my parent. They was puzzled and unsure how it's possible. But now, it's all gone. Haven't seen them for years now.