My hubby made the mistake of letting my parents loose in Lake Erie. She at first was just having fun sticking close to the beach, but then... she noticed a bunch of ducks a little futher out in the water so she started swiming towards them... and did not stop! She'd get close, and they would fly out further... well... Rick had to swim out after her because she would not listen to us. She was so tired by the time he got to her she tried jumping on his back, and pushed him under the water
(she is a GSD Mix about 75 pounds)
So... it was not a good experience. But if your dog is good and comes when called then it would be fun!!!