Steve panicked while we were snorkeling in Mexico a few years ago because he didn't know how to swim. After we got home, he signed up for swimming classes and has continued since then.
This time he signed up for a class on Saturdays at the community college near our house, and he can bring a guest to swim during the open sessions on Wednesdays and Thursdays. I have gone with him a few times.
I learned swimming when in high school. I always swim non-stop for 20-30 mins, then get out from the pool. I don't like soak in the water with chlorine too long. This one is six lanes x 75 feet pool.