A few things I've/we've done over 3 decades of Lab experience is if you have a pool, all of the ones I've had will swim year-round. Granted, I'm in South Louisiana, so the pool water temps don't drop out of the 70s, at least I doubt it. Any relatively clean body of water will do too, although here I have to pick and choose carefully. I would need to be institutionalized if I saw one of my dogs attacked by an alligator, so I don't let them swim in the Bayou any more, and thank God I was able to convince my wife not to let the dogs in the Bayou, her in the Bayou...optional...
Another tool we use is the Chuck-It ball thrower and the whistle balls. They even make one that glows in the dark, when you run out of daylight before they run out of energy.
The 2 puppies run around and play pretty rowdy with each other, so that helps too.