James,
I have freshwater shrimp in my ponds that survive and even thrive. The winters do not seem to kill them, but I am south of you but do get 50 degree water temps on occasion. Mine, like Gambusia, are there naturally and have never been stocked. They are very small criters and like Bill C. says, they require some weeds to survive predation...consistent with my grass carp low stocking strategy, the presence of shrimp and Gambusia and whatever else resides in those weeds are really a bonus for the food chain and best of all, its free, requires no chemicals or maintenance.
As to the hot tub....no room in the inn...all space going to Pacus this winter.
