We had a black lab for 13 yrs. He was a water dog, also. Have you ever seen them dive? My kids use to fill cans with rocks and throw it in the water. If he ran out of breath, he come up for air and have a stick or something and the kids would say, no,go down again and get the can and he always found it.
We took him to the beach and the seagulls were taunting him. They would land on the water, he would swim out to them and so on and so on until he was so far out he looked like a black dot. That time we thought we lost him, but he floated back. I loved that dog.