Imagine relaxing on a summer day next to a glistening garden pond with beautiful flowering plants and exotic colorful fish gliding by. You may have seen elaborate Japanese garden-type ponds, complete with bridges and waterfalls and thought, "Beautiful, but way beyond my budget!" Think again - there's a potential pond to suit any pocketbook.
Rather than a costly pre-formed pond, consider a heavy waterproof tarp, or a plastic half barrel, available in garden stores. I use the half barrel, which cost under $50 and has steep enough sides to discourage predators like cats and raccoons. The next important consideration is location. The pond should ideally be within reach of a garden hose to facilitate fill-ups. Ideally, it should also be accessible an outdoor electric outlet. You will need to set up an aeration/filtration system, unless you're planning to have very few fish (which few people are satisfied with). The pond should be in a partially sunny location. Too MUCH sun will encourage algae growth, making it resemble a large vat of pea soup. On the other hand, it's aesthetically pleasing to have the sun shining right to the bottom of the pond occasionally. Also, if you place it under a tree, you'll spend a lot of time removing leaves and other tree debris from the water. Finally, it should be in a place where it's safe to dig, i.e. no underground pipes, wires, etc. Digging the hole is the hardest past of the job.
JUST ADD WATER. Having dug the hole and placed the container, the next step is adding the H2O. Most tap water has chlorine in it, which will kill fish. Your options are to let the pond sit for 24-48 hours to let the chlorine evaporate, use untreated spring water, or to add chlorine remover (available at tropical fish supply stores). Natural ponds usually have springs or rivers feeding in and out of them, keeping the water pure. I use a pump and filter intended for aquarium use in my pond. Most people associate water lilies with ponds, but they can be pricey and as they require a pot with soil, also potentially messy. Inexpensive alternatives include water hyacinths (which produce beautiful purple blooms) and water lettuce; both of which are freefloaters - meaning no pots/soil required. Those "lucky bamboo" plants thrive in an aquatic environment. I bunch together a half dozen or so of them which rise out of the water like a reed marsh, and provide the fish with a shady respite area. I get 18" tall bamboos for $2 apiece at a local Oriental market.
Commercially available fish best suited for outdoor pond life across most of the temperate US are the closely related and similar-looking koi and goldfish. Prize winning koi can be valued in the thousands of dollars, and even small koi tend to be more expensive than similarly sized goldfish, so you may wish to stick with goldfish to keep expenses down. Moreover, you might consider so-called feeder fish; especially if your local fish dealer will allow you to pick and choose. This year, I purchased some feeders for 39 cents each at a large national pet store chain - many of them barely distinguishable from the $3.99 Sarassa red and white comets in a nearby tank.