There are many reasons to add yard ponds to landscaping, but the most common is to have something really unique as part of the landscaping around the home. They can be as big or small as the homeowners wants, and can afford, and can be made with a preformed lining or dug out by hand and coated with a lining. It also needs to be decided early on if yard ponds are going to serve as home for decorative fish such a Koi.