If you want Koi or goldfish swimming in your backyard, but don't want to go through the time and trouble of digging out a pond, then consider building an above ground fish pond.
The process for building an above ground fish pond is similar to one that you excavate. First, pick a spot. Keep it out from under trees, and in view of your home if you have young children. One advantage to an above ground pond is that you can put them on a deck or patio. Just be sure the structure can support the weight of the pond when it's filled with water.
Next, decide on the shape of your pond. If it's a standard shape, you can probably buy a pre-made liner. If not, you will need to purchase a plastic liner. Be sure the liner is sturdy.
For the walls of your pond, you can use brick, york blocks, wood, just about any material you'd normally use in landscaping.
You'll also need rocks for the bottom of the pond and a filtration system. You might have to wire your filtration system if you don't have an outlet nearby. The same goes for any lighting you want in your pond.
If you plan on stocking your above ground pond with Koi, remember that they can grow large. They'll require a pond that holds at least 1,000 gallons of water, which is about 50 square feet. Your pond will need to be at least 3 feet deep for Koi. Deeper is better as it will help keep the water temperature even. Also, keep in mind that domestic predators such as cats, raccoons and some birds favor Koi, so you may want to protect them with netting.
If you plan on stocking your pond with goldfish or some other smaller fish, your pond can be smaller.