The water garden and koi (Japanese name for the fish called a Carp) are a natural combination. Let's take a closer look at this beautiful and entertaining fish.

Although koi and large goldfish have certain similarities, koi are actually carp. They do grow bigger than even the biggest goldfish, attaining up to 3' (' = feet) in length under optimal conditions. They also come in a greater variety of colors and patterns. Their names bespeak their glittering looks, including living jewels, flower carp, or brocade carp.

They will even follow their owners around the pond for food morsels, and will allow friendly hands to gently stroke them. They can also live for years under protected conditions (i.e., exposing a koi to the local owl population will not aid its longevity). Koi can be horrifically expensive, although beginner fish can cost considerably less. Ideally your koi will breed to increase the population.

The most important thing to remember with koi and water gardens is that they require a certain depth. 18" (" = inches) is the absolute minimum and 2' to 3' is better. It must also be large enough to support koi, especially if you are fortunate enough to breed them. 1000 gallons is a minimum volume, which translates to a water garden that is 10' long by 8' wide and 20' deep. ( Goldfish can thrive in much smaller volumes of water and are a tiny fraction of the cost of koi.)

Also consider that we are not talking about a 8'x10' box. The koi pond should have shelves for shallower depths, which helps the koi at feeding time. The depth is also an escape hatch for frozen surface water or in case predators come too near. These shelves also serve to house bog plants in containers, making them a very common element in water gardens.

Koi do need some specialized equipment to keep them healthy. At a minimum they will require an aerating pump to keep the water oxygenated, and a filter -- mechanical and/or biological -- to comb ammonia and other harmful compounds from the pond water. Of course, the koi themselves will do a great job at keeping the local insect population down.

Assuming you don't have $2000 lying around to blow on a fish, you will probably be looking for less expensive sources for healthy fish. For example, look out for the shape. It should be broad at the shoulders and shaped like a torpedo. You do not want a koi that is string-shaped or eel-like. Buy one that looks and acts healthy. Reject fish with deformities, that are lethargic or swimming upside down (hello!), that are in isolation, or that have parasites. Also reject a koi that does not want to eat. Koi are notorious hogs when it comes to eating, and a koi with no appetite is a sick koi. And finally, look at the color - the more brilliant, the better.