What is a pool pond?

The basic idea is a hole in the ground with a tarp lining the hole. It is a red-neck pool on a really large scale. Our pool pond is approximately 45 feet x 15 feet. Our source for filling it is a creek that is higher than the pool pond. We filter the water as it enters the pool pond. When the water gets nasty we just empty the pool pond through a capped 4 inch pipe at teh deepest part and it drains into the lower creek. The pool pond is filled and emptied using gravity.