Little late here but I hunt with a Chessie and he’s got his vest on anytime the air or water temp is much less than 50. A lot of folks will say that dogs (especially chessies) are made for the cold and don’t need them, but I’d rather have a dog that is comfortable and enjoys jumping in the water than one that’s cold and miserable the whole time.
Side note: My dog lives inside. I suppose if you have a dog that lives outside in the cold he builds up a thicker coat that will keep him warmer. But I don’t know why anyone wouldn’t want their best friend in the house with them.