Koi (photo flickr-corrieb)
For some water garden enthusiasts, the best reason for having backyard ponds is to be able to raise koi or other fish such as the common goldfish. Both koi and goldfish are beautiful fish and relatively easy to care for. (Be aware, though, that there are different varieties of goldfish, and not all of them are as hardy as the common goldfish. Check before you purchase.)
Koi and common goldfish are indeed easy care backyard pond fish, but that doesn’t mean that they are “no care”. There are three important things to consider before introducing koi or goldfish into your backyard pond: 1) water temperature, 2) oxygen, and 3) predators.
Backyard Pond Temperature
Depending on your climate, you may or may not need to use a small heater during winter to keep the water in your backyard pond from freezing solid. It’s OK if ice forms at the top of your pond, as long as there is unfrozen water deeper down for the fish to swim in and a hole for oxygen. Do check to make sure your pond is deep enough to prevent it from freezing right down to the bottom during winter. If in doubt, install a small heater or pond deicer to prevent the water from freezing solid.
Oxygen
You’ll need to use pumps and filters to keep enough oxygen in the water to support fish life in your backyard pond. You may also want to use a pond skimmer to remove the big debris prior to filtering.
Predators
Backyard ponds can attract attention from predators such as (in North America) raccoons, birds (particularly herons), snakes, and domestic cats. These predators can decimate your fish population. Not only is this upsetting, it can also be expensive. You can minimize this problem by designing your backyard pond to have lots of places for fish to hide from predators.