They love to swim, especially to retrieve the aforementioned tennis balls. Pools require supervised swimming. He won't be able to pull himself up over the side, so he could exhaust himself trying to get out, then drown. Cracker loves pools, lakes, ponds, puddles. She enjoys retrieving and goes for recreational swims in our friends' pools.
Mud puddles are Lab magnets.
Cracker relishes any opportunity to disport herself in cool, clingy slime. Anything we regard as gooey, messy and dirty she sees as puddle-luscious. Luckily for us all, a Lab's coat is relatively self-cleaning. She does require regular brushing, especially if she's not been swimming in a day or so, because she sheds quite a lot. Labs are workaholics.