Second on the "good swimmer drowning" part. I once swam in a pool with a few cousins of mine. I was around 18 and just finished a life guarding course at school. One cousin was around 11 years old.

She was panicking next to me in the pool all of a sudden and climbed on top of me. She wasn't heavy but her human effort to grab and exert pressure to use me as a float to stay above water forced me under. It was hard to get back up for air, and very sudden to which I didn't have a ton of air to begin with.

I remembered training, which was to pull the victim down with you to short circuit their brain into letting go, and it worked. I was able to swim out from her area, surface, catch a breath, and go help her to the shallow end.