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How Deep Should a Fish Pond Be?

| Updated September 26, 2017

An outdoor fish pond is an attractive addition to any backyard landscape. While building your own fish pond might seem challenging, research and planning will help avoid errors. Koi fish and goldfish are the most popular fish for outdoor ponds. Koi fish are beautiful, though delicate and require extensive care. Goldfish are not as pretty as koi, but are more low-maintenance. However, both require a certain size pond in which to thrive.

Fish Pond Depths

One of the most important factors in building an outdoor fish pond is the size. Both koi and goldfish can grow to be at least 2 feet long. If the pond is too small, your fish might end up fighting and injuring each other.

If your pond is too shallow, water evaporation from the sun could leave the fish in the open air. Shallow ponds also leave fish vulnerable to predators like foxes and raccoons. The pond must also be deep enough that it does not freeze solid in the winter. The fish must have a space near the bottom of the pond to huddle during the cold months.

The best depths for koi and goldfish ponds are anywhere from 4 feet to 21 feet deep. Four feet of water will prevent excess water evaporation and keep predators from eating the fish. Steep, hard-to-climb banks will also deter predators.

In warmer climates where the pond will not freeze, 4 feet is plenty. In temperate climates with mild to cold winters, 7 to 8 feet deep is preferable. In places with extremely cold climates, 12 to 21 feet deep is the best.

It is important to match the length of your pond to the depth. A 4-foot depth should be at least 8 feet long. A pond 8 feet deep should be about 12 feet long, while a pond 21 feet deep should be about 17 feet long.