The AAP says: "infants younger than 1 year are developmentally unable to learn the complex movements, such as breathing, necessary to swim. They may manifest reflexive swimming movement under the water but cannot effectively raise their heads to breathe. There is no evidence to suggest that infant swimming programs for those younger than 1 year are beneficial."

The evidence for swimming lessons before 1 year is discussed in this article: https://sciencebasedmedicine.org/summer-is-here-and-infant-s...