Honestly, I cannot remember not being able to swim well. From my earliest memories, I felt very at home in water -- nobody could keep me out of it. During the summer, I just wore my speedo under my pants instead of underwear, because if I saw water, I was going to be in it. Spent untold hours in the Ottawa River (freezing cold, even in summer) and the Rideau River in Ottawa (a bit warmer), cutting my feet to shreds on the clam shells along the beeches and in the shallow water.
From my earliest memories, I could do freestyle (what we used to call "Autstralian crawl" back then), breast stroke, back stroke, butterfly. Can't remember if I did doggie style like most very young kids do, but probably.