I've raised labs for over 30 years. Depending on the weather, I've had pups retrieving tennis balls in the water at 12 weeks. But like Cessna states, don't force the issue. I don on a pair of hip boots and start in puddles then slowly move to deeper water. Make the first couple water presentations all fun and games. Just playing in the water. Once the pup's confidence builds, then start retrieves in shallow water and soon he will be swimming and not even know it. Be forwarned however that the first time or two you may have to go in after it cause he might not have his confidence level up. You may really have to get him excited to go after the toy.