i found this to be quite funny...
"Fish and other creatures including, but not limited to snails, hermit crabs, shrimp, and anemones, can and will find their way into your overflow and sump. Often, you won't even realize it's happened. Some of the fish might even find the water slide exhilarating. I once had a zebra goby that, despite my lectures, would make the trip several times a week before I finally managed to find an effective way to enforce the height restrictions on the ride."