There are several styles of koi pond construction, they can be used separately or combined to create a hybrid system.
Dedicated Koi Pond: A dedicated koi pond is constructed only to meet the needs of the fish. This type of ponds are deeper and will have a much larger filtration system, this types will give the owner the flexibility of using salt in concentrations from .05 to 1% which in turn reduces parasites, and provides stress relief for koi fishes and it also enhances the healing of wounds if any. Salt can be used in a dedicated koi pond since there are no plants, these high concentrations of salt will typically kill most aquatic plants.
Water Garden: A water garden pond generally incorporates live plants and doesn't use a gravel substrate. A slower water flow or water fall is provided in such a way that it doesn't disturb the ecology of plants.
Eco-System Pond: An Eco-System Pond is an simple economical construction style. Typically a waterfall and skimmer are used and a gravel substrate provides surface area for beneficial bacteria to grow. Aquatic plants are used in an Eco-System pond which contribute to pond health.
Hybrid Pond: A hybrid koi pond uses any and all elements of pond styles, which may have additional equipments such as UV sterilizers and artificial aerators etc.
Mud pond: A koi mud pond is generally used by more experienced koi keepers. In this type of construction use of normal filtration will not work. Fish keeping in these types of tanks are very complicated process. It will require special skills and good management techniques to do the same.