this is great....im wanting to do a dry creekbed with a pond on offset center of the creekbed. this is my big landscape feature for next spring! my backyard slopes so that wont be too bad for gravity to work, just incase we get huge amounts of rain. will be planting nana trees in the"creekbed" along with other tropicals. i want the,"there once was a rive flowing here" look with a small pond in it. are the only type of fish that can be put in a pond koi? or can you put other types of fish in a pond?