There are many canals here in Florida that are freshwater, and the St John river system runs from just south of Melbourne, Fl, all the way to Jacksonville, Fl. The area I was fishing is part of the St John system.
As far as the temps go, a few years back we had a bad freeze here, temps went into the 20's at night for about 4 days. I was amazed at how many Tilapia we saw that were stunned from the cold, never knew there were that many in the local lakes. They were everywhere, just lying on the surface, stunned from the cold.