I swim outdoors in a pool heated to 82 degrees year round, even when temps dipped in the 20s earlier this year. But, I do it for training not recreation.
That being said, I have been every January except 2010 (the yeah they had snow flurries) and every year we have been for marathon weekend we have been able to swim and enjoy the hot tubs.
The last two years, on multiple days, we have been able to be poolside in normal pool attire (bathing suit, no shirt, etc) and been perfectly fine with temps in the 80s.
BUT, that is above average and you won't know until closer.
Pack for it all and dress accordingly from day to day.