The Icky Pool

There is a pool on the property that is in pretty rough shape. It needs a new pump and some severe cleaning. Currently it is nothing more than a breeding ground for mosquitoes. And my mother-in-law swears she saw something moving in it. I really hope it's a frog or turtle and not a snake.

We poured a gallon of bleach in it already to attempt to kill things off before we even attempt to clean it up but I have no idea what the next step would be.

Any suggestions on how to get this cleaned up safely?