Moving Black Shapes

I live in a condominium that has a large swimming pool. For virtually all hours of the day, it is deserted. Most of it is under shade, so from the side of the pool, nothing is visible under the surface, which is nearly a perfect reflective surface. Except for the moving black shapes. These are actually the pool drains. I grew up at a place like this, and it too, had a pool with those moving black shapes. Once, when I was 5, I swam in that pool. I cold hear the sucking of the moving black shapes. I swam across the shallow end. And I felt them sucking me in. Edit: I also remember nearly drowning that day. That must be it.