"We can still work on your swimming together! Besides, it'll give us something fun to do in the water when it warms up."

And he always likes having company in the water, both because the company is nice and because it's a good idea to have back up in case things go wrong. Sure, it's safer for him when it's warm enough that he can swim at peak performance, but that doesn't mean there aren't still dangers in the water in the summer, too.