Last year it was neoprene splitting cold(-10) and I got into the water to pick up a dead duck and sent the dog after a cripple. I went in all the way over my head. My shotgun froze stiff, luckily I always carry a change of clothes and quickly got dried off, even stayed until my partner finished his limit.
My dog loves the cold, he will ice up at times but you can't drag him off the river.
These two will bird dog for me but it has to be relatively warm to let them tag team the ducks.
When it is really cold I let my hunting buddies break the ice and pick up the decoys while I pretend to be busy with the camera.