I took the basic (open water?) license in Australia, and the group were sent into a pool to tread water for 20 minutes or something. Now, I can barely swim. Really poor buoyancy and bad technique I guess, so have never really learned.

If the instructor had looked away from the TV for a second he would've seen and flunked me, which would probably have been a good thing. I'm stupid. Went through with it and out on a couple of dives which I enjoyed greatly, but now ten years later still haven't dived again and won't until I can swim. Having kids does stuff to your sense of self-preservation.