The Minimum Depth of Ponds for Fish in the Winter

Fish ponds add a beautiful dimension to landscaping on any scale. Whether the pond is large or small, it must have adequate depth for fish to survive the cold winter months.

...
Backyard ponds must be deep enough for fish to survive the winter.

The Small Pond

The area a pond covers depends largely upon the size of the yard or garden. Whether a backyard fish pond is 3 feet or 8 feet across, the recommended depth for the survival of the fish is between 30 and 48 inches.

Koi Pond

...
Koi ponds should be at least 3 feet deep.

The ideal depth of a pond that supports a population of koi is 48 to 60 inches, although koi can survive with a minimum depth of 36 inches. That depth offers the koi protection from wading birds and also allows for a more uniform water temperature.

Cold Water Ponds

...
Large ponds support more aquatic life, but require greater depth.

Ponds of 1/2 acre or more can support more fish and aquatic plants, but require greater depth. Cold water ponds that are spring-fed need to be between 8 and 10 feet deep, while ponds that are not spring-fed should have a depth of 16 feet.

Warm Water Ponds

The water supply for large warm water ponds comes from surface run-off. The Monroe County (New York) Soil and Water Conservation District recommends a minimum depth of 8 to 10 feet for such ponds.

Other Considerations

...
A portion of a pond must be kept free of ice.

In addition to providing a proper depth, a pond owner should make certain to keep some of the pond's surface area clear of ice. This is necessary for a proper exchange of gases, allowing toxic gases to escape while allowing oxygen to enter.