Labrador retrievers love water and I honestly don’t know how you can stop a Lab from sitting in water, especially if it’s hot outside. I guess I’m wondering why you would want to do so. Regardless, trying to prevent a lab from going in water is like trying to make yourself stop sweating.
Labs were originally bred for retrieving birds that were being hunted for food or sport. I guess you try to avoid taking your Lab near any water. Or you could try to have special towels to dry him off and have a nice place for him to dry out. Good luck!