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Building a Backyard Koi Pond: How We Built Our Little Water Garden Around Rocks and Under Trees

Anthony enjoys spending time in the workshop, kitchen, garden, and out fishing. Many of his DIY projects are featured in his yard.

Our Pond is a Very, Very, Very Fine Pond

Our small backyard pond is home to goldfish, koi and frogs

Our small backyard pond is home to goldfish, koi and frogs

Building a Garden Pond Is a Fun and Rewarding DIY Project

Our small garden pond is tucked between an outcropping of natural granite boulders and under several large oak trees. While most guides for creating water gardens and backyard ponds recommend building garden ponds on a flat, level area in full sun and away from trees and rocks (and this is very good advice), our yard does not offer such optimal conditions. But this did not stop us from building a successful, unique and beautiful garden pond that is filled with healthy plants and fish, and has rewarded us with years of enjoyment.

Left behind from the retreating glacier that covered the Northeast during the last Ice Age, the granite ledge and large rock outcroppings in our backyard provided a dramatic backdrop for building a little garden pond. A gap between two boulders left a natural trough that was perfect for building a little stream to trickle down towards the pond, cascading over the edge of a waterfall and then spilling into a small pond that we dug out between the rocks and contained with a cinder block retaining wall.

Building this small garden pond in an area surrounded by ledge and boulders, under trees and on a slight slope was a challenging project, but it was a lot of fun too.

Plants help to keep the water clean, give fish shade and places to hide, and they look good too.

Plants help to keep the water clean, give fish shade and places to hide, and they look good too.

Preparing the Site

We used a garden hose to lay out the perimeter of the pond. When building your garden pond, outline as large an area as possible; though the pond may seem huge initially, most pond owners wish that they had made their pond a little larger and a bit deeper. Our small garden pond is a teardrop shape, approximately 11 feet long and six feet across at the longest and widest points, and just over three feet deep.

Since we were digging the pond into a slight slope and around huge chunks of immovable granite rock, we marked the highest point that would indicate the surface of the pond, and then used a string with a line level to determine which sections of the pond's edge were below this point. This gave us an idea of the angle of the slope, and the height of the retaining wall needed to contain the low end of the garden pond.

The low point of our garden pond was nearly 24 inches below the highest point near the waterfall. To contain the water on the low end, we built a low retaining wall with dry, stacked concrete blocks, and then covered the block wall under a berm of dirt.

Digging in

Digging the hole for our small garden pond was a manual effort, one shovel full of dirt at a time. Though a renting or hiring backhoe would have made the job easier, locating our pond between the large boulders made it difficult to position a backhoe around the rocks to help with the digging. The end result was a lot of shoveling by hand.

We dug down as deep as we could until we hit a "floor" of ledge rock. We used the dirt removed from the hole to backfill the outside of the retaining wall. The resulting pond is just over 3 feet deep, which is deep enough to prevent it from freezing solid during the winter. Deeper water also helps the pond to stay cooler during the summer months and keeps the fish out of the reach of predators, such as herons and raccoons.

The waterfall in our small pond pours out between natural outcroppings of ledge

The waterfall in our small pond pours out between natural outcroppings of ledge

Laying the Pond Liner

The bottom and sides of the pond are layered with newspapers and old carpet padding to protect the pond liner from tree roots and sharp rock. We purchased a thick rubber roofing liner from a commercial roofing company that we found online, and used it to cover the bottom and sides of the pond, adjusting, fitting and smoothing the liner to fit into all of the nooks and crannies. The liner extends up and over the edges all around the pond and well above the highwater mark.

The waterfall and stream were lined with more of the rubber liner, cut with a razor knife and fit with sections of rubber liner. We used a specially formulated exterior grade rubber adhesive (often used for rubber roofing) to glue all of the liner seams together, creating a watertight seal. We used the rubber adhesive to glue the rubber liner in place along the rock outcroppings. The rubber adhesive bonded well with the rough texture of the rock, and it has held up well for many years without any leaks.

Add Water

We added layers of chunky field stones to create a rock wall with shelves for plants, and caves and crevices for the fish to hide. The spillway for the waterfall was formed by carefully selecting and positioning smaller rocks. More rocks and pebbles filled in the gaps between the bigger rocks, creating natural cavities and helping to further hide the retaining wall.

As the pond filled slowly, we paid close attention to the liner. Keeping the liner taut and pressing the liner down against the bottom and up along the sides of the pond as it slowly began to fill with water kept the liner in contact with the dirt floor and reduced wrinkling. Tucking the liner under the rocks that form the capstones along the top edges of the pond holds the liner in place and finishes the edges with a natural look.

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The water was murky when we first filled the pond but after a couple of days running the pump and filter, the sediment settled and the water cleared. We waited a couple of weeks before adding fish, giving the pond a little time to naturalize a bit. A waiting period is especially important when using city water, to allow chlorine and other additives to evaporate, and for the water temperature to moderate to your local climate.

After many years, this unconventional garden pond is home to a small but healthy population of koi, goldfish, frogs, and insects. The aquatic plants thrive, though the mostly shaded environment limits the blooms of the hardy water lilies which require full sun. Even with these limitations, the pond and stream offer a year-round water source for the local wildlife. So don't let less-than-ideal yard conditions stop you from building a small garden pond. The results are worth the efforts!

Our Small Garden Pond

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Koi and frogs enjoying the pond.

Koi and frogs enjoying the pond.

Buying Pond Fish for Your Garden Pond

A healthy fish has a better chance of surviving the transition and travel from a breeder through distribution in the pet trade and ultimately to your garden pond. When shopping for pond fish, it is important to buy from a reputable and qualified dealer. The big pet retailers may offer the lowest prices on koi and goldfish, but selections of their stock are usually limited to the more popular species that sell in higher volumes. Aquarist specialty shops, koi breeders and garden centers are more likely to cater to intermediate and advanced hobbyists, and these specialists often carry more unusual and exotic types of koi and goldfish as well as the standard breeds.

Check the Tanks

Examine the condition of the tanks carefully before making a purchase. The tanks should be clean and well lit. Some retailers use a centralized filtration system, while others use individual filters in each tank. Both have advantages and disadvantages, and either can be effective filtration methods when maintained properly. Look for clear, moving water without accumulations of debris. Cloudy water or dead fish left in the tank are strong indicators of problems and should be avoided.

Look for Indicators of Poor Health

When selecting a fish to buy, look for active individuals with intact fins and bright coloration. Ripped fins can invite pests and diseases, while dull colors or lethargic movements are indicators of poor health. Even the common Comet goldfish have distinctive coloration, fin structure, and movements which can give an indication if a fish is stressed or unhealthy.

After identifying your fish of choice, always ask the salesperson to scoop out the specific fish you have selected. Even in a crowded tank with active occupants, it is relatively easy for an experienced salesperson to single out and net your selections. If the store is busy, it is often to your advantage to let the salespeople help the other customers first so that they will not be as rushed to catch and bag your fish. Ask the salesperson to use large plastic bags and only place one or two fish per bag. The more air and water in the bag per fish, the longer the fish can stay in the bag and the less the temperature of the water will change during the journey home.

Adding New Fish to the Pond

It can take a few days for a new fish to adjust and join the rest of the school.

It can take a few days for a new fish to adjust and join the rest of the school.

Give the New Inhabitants a Good Start in Their New Home

Follow These Simple Steps:

Now that you've purchased new fish, it's time to add them to your pond!

  1. Place the bagged fish into the pond as soon as possible, and then let them float around in their bag for at least 20 to 30 minutes. This time will allow the temperature of the water inside the bag to equalize with the temperature of the water in the pond.
  2. If your pond has a shallow shelf, stand or wedge the bags upright and open the top for fresh air water. Adding a little pond water into the bag will help the fish to acclimate further to the pond water.
  3. After the temperatures equalize, gently tip the bag into the pond and allow the fish to swim out. It is not uncommon for the newly introduced fish to seem disoriented, and swim down towards the deeper and darker sections of the pond. It can take a day or two for the new occupants to adjust to their new surroundings and join the rest of the school.

Visit Another Awesome Koi Pond

Beware! Bull frog eat fish!

Beware! Bull frog eat fish!

Bullfrogs are Carnivorous! (Our Bullfrog Story)

Bullfrogs were welcome at our pond—until we saw one attack and eat a koi fish! If you keep koi and goldfish in your pond, beware of hungry bullfrogs.

Purchased from a local gardening center, we added several bullfrog tadpoles to our pond over the course of several years. Bullfrog tadpoles are large by frog standards, and each plump tadpole was about 4" long when released into the pond. Unlike many frog and toad species that morph from tadpole to adulthood in a single year, bullfrogs spend the first year of their lives as tadpoles. They happily rooted around along the bottom of the pond and between the rocks, searching for food and picking at the algae.