How Deep Does a Fish Pond Need to Be?

Fish hobbyists and aquarium enthusiasts that want to take their love of the aquatic to the next level are often curious about keeping a backyard pond. Ponds add a beautiful aesthetic to any garden and offer opportunities to raise certain types of fish and plants that are difficult to keep in a regular aquarium environment. However, most people who have limited space to work with often wonder how they can obtain all of the benefits of a home pond without digging up their entire yard. The good news is that ponds can absolutely be set up to operate on a small scale. So, how deep does a fish pond need to be?

The minimum depth for a backyard pond is 2 feet deep. This gives space for some beautiful aquatic plants and can accommodate smaller pond fish such as goldfish. However, if you are planning on keeping a larger species (such as koi) or you live in a very cold region (colder than zone 5) you will need to have a deeper pond of at least 3 feet- and 4 or 5 feet would be better! Larger fish will need a larger depth because they take up more space, and very cold climates need the extra depth to keep them from freezing solid. If you are flexible about the types of fish and plants you would like to keep, then you can absolutely find a backyard pond that will work for your space. If you are set on a traditional koi pond, you will need to make an extra effort to set up a pond that will accommodate them.

Koi Pond Requirements

Koi fish are probably considered one of the most quintessential pond fish species. With a spectrum of beautiful colors and fin shapes, it’s easy to see why they are so popular. It’s hard to believe that these lovely fish are descended from ordinary carp, but when it comes to living in cold and rugged environments, koi are just as hardy as their wild cousins. Their hardiness is what makes them a great candidate for pond life. However, they do have some basic needs that need to be addressed when building a backyard pond.

We already mentioned that a koi pond needs to be a minimum of 3 feet deep, but how big does it really need to be? A minimum overall size for a koi pond is 1,000 gallons, and often more. Koi are large fish that live very long lives- averaging 20-30 years! In ideal conditions, they can live even longer, and they continue to grow throughout their lives. The largest koi can top out at 36” long! With sizes like that, it’s easy to see how a 1,000-gallon pond can be on the small side. To put that in perspective, a 6-foot by 8-foot pond that is 3 feet deep will yield a little over 1,000 gallons, and fit about 4 koi fish. You can scale up the number of fish by using the guidelines of adding 1 inch of fish per 10 gallons of (good quality) water.

This is not to say that a small yard can’t handle a koi pond. In fact, many natural ponds have undulating depths- a shallow end and a deep end, so to speak. If you are hoping to accommodate more than a few koi, you can increase the volume of water in your pond by digging a deep end of 4 or more feet. In fact, a deeper pond can be helpful for your fish in the summer and winter months, when the weather can affect the temperature of the shallow water near the surface.

In addition to size, like any fishkeeping environment, you also need to consider filtration and oxygenation in order to keep your fish healthy. This might seem unnecessary because there are ponds found in nature, but your fish will live much longer and healthier lives when you pay attention to the water quality. There are many great quality pond filters available that are designed to keep things clean and establish beneficial bacteria colonies to combat algae. Adding a waterfall or fountain is another great consideration because it will oxygenate the water and keep things flowing to prevent stagnation.


Goldfish Pond Requirements

If you simply don’t have the space for a koi pond, goldfish make a great alternative pond fish and come in the same beautiful colors and shapes as koi. The rule of thumb for goldfish kept in aquariums is that you will need 20 gallons of water per fish. For ponds, you can use the same guidelines as with koi- 10 gallons per inch of fish. A good minimum pond size to aim for with goldfish is 500 gallons.

The minimum depth for goldfish, or other smaller pond fish, is 2 feet deep. However, you will need to consider your climate when digging your goldfish pond. Cold hardy fish such as goldfish and koi go dormant during the winter months and can tolerate frigid temperatures, however, if the pond freezes solid, your fish will die. If you live in an area that is colder than zone 5, you will want to provide deeper areas in your pond to ensure that there is at least a foot of liquid water for your fish to hibernate in.

Digging a Pond: The Basics

The easiest way to get started with building a pond on your property is to [amazon link=”B003TO45FU” title=”purchase a pond kit” /]. These kits provide the basic items you will need for your project and you can choose from a variety of sizes and levels of finish depending on your budget. The most basic kit will likely include a pond liner or tub, a filter, and all connecting tubing and hardware. You can also source these products individually yourself. There are additional items that you may want to also include such as de-icer (for the winter months), protective netting, or fencing to keep out predators.

Once you have your supplies, you will need to visualize the shape and layout of your pond. You can make the outline with rope or spray paint. During this step, you can also make some marks to indicate any slopes or changes in depth. For example, many folks choose to keep a shallow shelf of soil on the perimeter for aquatic plants. Use the outline as a guide to dig your pond. (Don’t forget to check with your utility providers to make sure that there are no cables or pipes buried under your chosen spot!)

Once the hole is dug, you will want to place the skimmer and filter and connect any tubing. Next, proceed with installing the liner. This can be secured in place with a few boulders or heavy gravel. You will want to make sure that the edges are secure to prevent leaks. Next, add your waterfall filter or any other hardware that will need to be secured to the liner. Follow the instructions unique to your kit to be sure that the liner is well secured to the filter and skimmer. Once the liner is firmly in place, you can add gravel and any other decorative rocks to really get the right look for your pond.

Like a regular aquarium, make sure that you let the filter run and cycle for a few days after adding water. This will give the pond some time to establish beneficial bacteria in preparation for your fish.


Ponds are a fantastic addition to any landscape and can be an exciting adventure for a fish enthusiast. Ponds have a great aesthetic and often will add value to your property. When established properly, ponds are a unique ecosystem that is a great environment for fish, plants, and local wildlife. They are among some of the best environments for keeping koi and goldfish, which both require a lot of space and are hardy enough to live in unheated waters. Koi are the most popular pond fish, but it’s important to keep in mind the space requirements that they need to live long and healthy lives. Goldfish are a relative of the Koi and make a great alternative pond fish for those who can’t sustain a larger pond on their property. No matter what choice of pond fish you select, it’s very important to dig a pond that is deep enough to accommodate your fish. 2-3 feet will be the minimum depth for those looking to keep koi or goldfish, and even deeper depths will be required for those who live in colder regions. Building a pond from scratch is a pretty straightforward process and there are many kits available that come with all of the required equipment for creating your own unique pond. Similar to an aquarium, all ponds should have adequate filtration and oxygenation for optimal health. Now that you have a solid understanding of the depth requirements and other basics for a pond, you will be able to create your own outdoor water garden with peace of mind.

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Rick Kesler

I'm Rick and I've kept freshwater fish for over 5 years now. My main tank now is a 55-gallon tropical freshwater tank and my wife and I both just love watching all of our different fish while they swim around, some schooling and others not. I've also learned a lot about what to do and what not to do to keep our fish healthy and happy.

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