one worm isn't bad. My first year owning my pool I didn't put any kind of cover on it during the winter. SO no cover, no chems, no running pump for about 6 months. It rains a lot and i notice a lot of worms around the pool deck during the winter. When the summer came and I was cleaning the pool i probably pulled out 100's of dead worms off the bottom of the pool. The smell and the slime were horrible...i debated if i'd ever swim in the pool again. After a few weeks it was sparkling blue and clean, but every time i get in i think of the dead worm smell.