A koi pond should usually be at least 3 feet deep to keep the fish happy and safe. This depth helps protect koi from predators and reduces the risk of water temperature fluctuations, which can be harmful. In colder climates where ponds may freeze, a depth of 4 to 5 feet is recommended so that the koi can overwinter safely in the deeper, warmer layers.
Deeper ponds also improve water quality by allowing more room for waste to dilute and for proper circulation. While shallow ponds may seem easier to build, they often lead to more maintenance and stress for the fish.
