I did lightly toss Cider in a creek when she was younger, she was pretty upset and it was a life saving action for her to get to shore, I felt awful.
She wears her life jacket willingly. She's not always amused to be in the pool though, she needs to be occupied and she won't ever just float, her legs paddle unless she's standing on something stable (like you). We often play fetch in the pool so she's got something she would like to do.
We wentto a friends cottage this past summer and we swam off the dock together and such.. They have a pricate beach.. I was playing fetch with her and I threw the ball too far, she actually kept going and swam after it, I was a proud mom, she evidentially learned a different motion with her paw and leg position being supported in the life jacket