If I don't get my levels up early in the season, I start finding posters around the neighborhood "Party @ Kim's, Frogs Only!" If I don't get them all out before I start adding bleach, they'll die. I had a couple jump in while I was slamming (didn't see them jump in) and found them floating the next morning.
We also had one summer, chipmunks that thought they were lemmings (I know, it's only a misconception about the mass suicides lol)! We would be sitting by the pool, you would hear a faint splash, and a new chipmunk was in the pool. If you don't catch them quick enough, they drown.