Something similar is fairly common in South Florida, since so many homes have pools.
My oldest daughter was literally "thrown" in the pool when she was about three months old. We hired a respected professional to do it over several visits, as I was petrified at the time. After the initial throw, she begins to motion the child to her and the infant will swim. It's instinctual that an infant swim and float and despite mom's pain
my daughter was loving the water and swimming from the get-go.