The preformed pond is molded plastic or fiberglass. It comes in a defined shape, everything from a simple oval to pretty elaborate things. They are good starter ponds for people that don't even really know whether they want a pond. So you just have to dig the shape of the tube to put the preformed pond upside down on the ground. You dig a hole, then, you drop the liner in. The pond is installed; it's that easy. You put in a little pump and maybe some rock work and plant. After that, you are done. They are not very deep so they certainly cannot sustain Koi. Once the gold fish start getting bigger, they quickly over power the preformed pond.
