Pond Frog

Question
My daughter & her husband just bought a house with a Koi pond.  In the pond, I have seen a dark colored frog and it looks like it has smooth skin.  I've seen the frog twice and in was sitting on a rock in the water (half submerged). What is the best way to determine what kind of frog this is and if it is a hazard to the local environment?

Answer
If you send me a photo at help at fishpondinfo dot com as well as where you live, I may be able to tell you.  If the frog is native, it's not a hazard aside from the fact that it will eat things to stay alive.  It sounds like the frog is aquatic.  In the Eastern US, that would probably mean it's a bullfrog or green frog.  Where do you live?  I have photos of some frogs on my site at http://www.fishpondinfo.com/frog2.htm
Good luck!