I agree that it won't hurt fish. However, it is hard to see. I have noticed that flake fish food will float and spread fast and will follow direction of flow and is easy to see; win, win, win, win.

@joe009 I just went on my lunch break and it did stop- at least I think it did. I'm guessing it's right behind my rocks- i'll have to remove them tonight- I don't want to keep filling it up when it starts freezing! :( Thanks!

nicole- after you remove your rocks, put a good thick liner behind the rocks, not just a pool liner.epdm pond liner works best,with a backing under the liner, to prevent tears, and cup the edges so the water does not run off the sides

I should have mentioned this earlier. You could also have a plumbing leak or break in your pump to waterfall line at the stable water level. Of course, you would probably have to rip mostly the same stuff apart to find it.

I found it abut 2 weeks ago.. a huge slice of slate fell and jabbed a huge hole. I know there was another little one bit this one did it in. :( we bought a huge aquarium and put our fish in fir the wunter. Once the ground thaws well be making a new pond with a new liner. Thanks everyone for ur help!!!

Oh wow spell check! Lol

Thanks for the update. Its always nice to learn what caused problems. It is often recomended that heavy rocks be supported by an extra (inside the pond) layer of liner or other strong material to prevent tears. It sounds like an even stronger support would have been needed in this case however.