Building an outdoor Fish Pond can be a daunting task.  There are limitless options, and countless methods to do so.  The most important process in building a Fish Pond is the thought given to its design.  This Pond is going to be a fixture in your yard hopefully for years to come, and it will be very conspicuous.  It also will require maintenance on a consistent basis.  The pond will require electricity to power the pump, lights, and some filtration devices.  The pond will need water for top-off and exchange purposes.  Be wary of excessive sunlight, as it will grow algae, or excessive tree cover, as the falling leaves will pollute the Fish Pond.  Predators are an often overlooked component.  If you live in an area susceptible to predation, be sure to leave an open area around the pond, as they are less likely to hunt pond fish without sufficient ground cover.  Also consider some cover for the fish themselves, as predatory birds prefer open water areas.

Selecting the shape of the pond is mostly for aesthetic reasons, though function should also be considered.  In hibernation regions, the pond should be deep enough to allow for hibernation.  The Pond will require a consistent flow, so areas should be constructed to allow sufficient flow.  If desired, and overflow should be created in a remote region that can be hidden to keep the natural look and feel of the Koi Pond.  The Overflow will contain an additional mechanical filter, similar to that of a swimming pool overflow box.  The overflow can then be plumbed into the pump, either submerged within the box or external.  The pump will move water discretely to the filtration system and then strategically fed back into the Fish Pond, preferably in multiple locations to maintain a consistent flow.  The Filtration area should contain an extra valve that can be used to drain the pond for cleaning or water exchanges.  Electricity will be required in the filtration area, and should be put into place prior to construction.  An electrician can assist you with this. 

During rainfall, runoff water will flow over sloping areas, carrying waste, pesticides, fertilizers, and other contaminants.  If possible, the Pond should be constructed in a location that is guarded against such occurrences.  It should also contain a small shelf area around the perimeter in which to places rockwork or plants to hide any liner or other construction materials.  The rockwork can be purchased through a quarry, or can be naturally created using the rocks unearthed during its own creation.   The excess dirt and rocks can be easily disposed of by creating a stream or waterfall directly adjacent to its location.