D.O.P.-T.

On walkies, we sometimes pass a city pool in the park. They have blue covers on a huge reel for unwinding over it in the off season to keep leaves and other debris out. Last year they evidently cut costs by never doing this, and it was quite a job to clean the pool out. This year there is a long electrical cord - also blue - snaking into the deep end, and occasionally one can see that it goes to a pool Roomba. It seems to be working - the bottom of the pool is clear.