Laika even goes into the water, with tempratures far bellow freezing point. So, the water isnt the problem, but if they come afterwards out of the water, and keeping them warm is the tricky part
So, after a cold swim, just keep them running to get warm
Labs were originally bred to swim in freezing cold water, so I don't think it's too much of an issue for most Labs. That said, my Abbey is a mix, and she doesn't have the proper coat of a Lab to keep her warm, so when it starts snowing, I don't let her swim anymore.
Cold Tail is NOT caused by cold water. Although it can predispose some dogs to it. Cold tail is more a descriptive term for the tail itself in it's injured condition... the dog will be reluctant to use the tail and will carry it low to the body. Aspirin and rest usually puts things right in a few days. FWIW my dogs have gotten "cold tail" swimming in 90 degree water in the middle of the summer.
My dogs swim in water that goes to about 42 degrees in the winter. They enjoy it
Yes, labs are bred to swim in freezing water, so it really isn't that much of a concern... especially where you live.
Sammi goes swimming in snow filled rivers on a regular basis - never seems to bother her. She has had cold tail once, so I do keep an eye for that just in general, but it was almost 2 yrs. ago and never a problem since.