As I understand it, most baby/parent swim classes don't necessarily teach a baby to swim, but instead helps them to be comfortable in the water, the next stage is water safety, and then teaching actual swimming. That is according to classes.
My friend that did those classes did just that, blew in their face which causes them to hold their breath and then put the baby right under. The other important technique is to continually smile yourself, especially when you pull the baby up out of the water. They see your smiling, enthusiastic face and think, "oh yeah! FUN!"......I never did this......
Just heard about it. And have seen it.
Dd was pretty shy of the water until 2 & 1/2. We started going to the ocean regularly at age 2. Then one day, she just went under all on her own and knew exactly what to do.
There is a beautiful Russian video about water births and it also has scenes of a baby on a big sister's back swimming in and under the water like dolphins. It is beautiful! There is also a beautiful book by Michel Odent, called "Water Babies".
If you are inspired, I would either take a class or get a book so that YOU feel completely comfortable and go for it!
I remember something about doing it by 2 months of age too. (for instinctual purposes)