Can a red ear slider hibernate in a Massachusett pond?

Answer 1

It's all about acclimation. Meaning, you can't just chuck him out there in the middle of winter and expect him to live.
IF he lives outside, near this pond, all the time (never spends any time indoors), he should be fine.
He has to live naturally in the environment 24/7 so that his natural body processes adjust properly to the changing weather.
BUT
I wouldn't risk it. Let him live outside until mid-summer. Then catch him up in an outdoor pen and wait for him to go into hibernation, then put him in the garage for the duration of winter.
OR
Keep him indoors and don't let him hibernate at all. If he's an indoor only pet, keep his light and heat sources on and he won't hibernate. This is best for caged pets. It doesn't hurt them.

Answer 2

If you are thinking about releasing a pet, it is not a good idea- that is not the native range and it will not do well.

Even in the places where Red-ears are both native and hibernate (in most of their range, they don't ever deal with freezing weather), this is the wrong time of year. They enter hibernation in the late fall after scouting out a good spot.