I was right! Terminal stupidity. The clues are:
1. People in a pool that was too cloudy to see anything - who wouild swim in that?
2. Lifeguards that allow such a pool to be used.
3. A non-swimmer who plays at the deep end of a 12' deep pool.
4. Witnesses who see a victim go under and not come back up, yet do nothing and don't tell the lifeguards.
5. Companions who don't think anything of someone going missing at a swimming pool.
6. Pool management that doesn't check the pool is empty when it closes and that allows a polluted pool to be open to the public (even a public as lacking in discrimination as that in Fall River).
If it weren't so tragic it would be great comedy.