How to Build a Koi Pond in Your Backyard

Bill Taylor
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What You’ll Need To Get Started

Most states don’t require a permit but you should check with your local building code officials. Some states or counties may require a permit during the construction and installation stages, so be sure to check before you begin.

If you don’t have a very big budget, you can get the basic items you need at home. Here are some ideas:

  • Pond liner
  • This is the most important feature as no matter how you construct the pond, it will be useless if you don’t have a liner to protect

The soil and plants from damage during construction and to prevent leaks into the surrounding soil.

It is recommended to use high density polyethylene (HDPE) liners. Be careful you don’t use opaque liners which reflect heat and can raise the water temperature. UV inhibitors and oxygen inhibitors can be added to the liner depending on the season and the pond water temperature. Detergents and cleaning solutions can damage the liner and reduce its useful life. Also, check for cracks and punctures that could affect the capacity and the life of your liner.

Old Tires

Your local auto repair center should have old, worn tires they don’t want anymore. They can function as the perfect liner for the edge of your pond.

Step One: Evaluate Your Space

One of the most important things to do when deciding to make a pond is to consider the amount of space you have available. Not all ponds are the same size. Depending on their intended use, a pond made for a single fish may be several feet wide and a pond intended to be a habitat for fish is going to be much larger. As you consider the space you have available, you should also consider how you plan to use the pond and what type of fish you are going to keep in it.

The main types of ponds are cool water ponds and warm water ponds. Cool water ponds are waters that are near the freezing temperature. If you live in an area with both warm and cool water species of fish, having a pond of each variety offers the best of both worlds. A warm water pond houses species such as koi, goldfish, catfish and other species that prefer warmer waters, like bullfrogs. You may be surprised how many options there are when choosing a species for your pond.

There are ponds that are created on a concrete slab or low lying areas where soil is not recommended because of the depth of the water. If you have a large enough space, you could also include an area where water flows over a series of pumps to create a waterfall. This is a beautiful feature that also adds a soothing sound for you and your fish.

Choosing Where to Place Your Pond

If possible, position your pond in a shady area to reduce the sun's temperature. This will allow you to enjoy longer swimming hours each year. If you are experiencing problems with aquatic vegetation, however, consider building your pond in an area that receives daily sunlight to help decrease the growth.

If building your pond near a structure, ensure that the roof is not near an edge that may break. If building a footbridge to your pond, ensure that it is substantial enough to hold the weight of the bridge itself as well as any additional weight of a child or small adult that should happen to cross it. If you are building a footbridge, I also recommend installing rope handrails to increase the safety.

Ensure that there is a solid, natural surface underneath your pond to support its weight and to keep it in line with your landscape design. The surface should also be able to be leveled to allow for a consistent depth in your pond.

Determine How Big You Want Your Koi Pond

In order to design and build a koi pond in your backyard, you first need to decide how big you want your pond to be. It used to be that koi ponds could only be built in a substantial backyard with plenty of land, but that is no longer the case. Today, a partial-landscaping company can install a “formal” koi pond, complete with tiered heights, in less than a day. Your pond can be a square or rectangular shape; semi-circular; and anything in between.

Some people choose to have more than one pond. These ponds should be far away from each other, so that one fish infestation, disease, or predator doesn’t affect both ponds.

Step Two: Start Digging

To get started, you'll want to do a little measuring so your pond is level and so you have enough room for it to fit. You'll need to dig a hole that is at least 12 inches wider than the pond that you hope to place. It is easiest to dig a circular hole and then put the sides around the hole. Choose a place for the pond that does not have a lot of sunlight on it, if you want a number of fish.

Rocks and wood can be used to make the pond fit in better with the rest of your backyard.

The bottom of the pond can be lined with gravel and rocks, which will make for a more realistic-looking pond. You will want to add at least one hole for drainage near the bottom of the pond.

Clear Space

First, you must identify a location for your pond. Not every spot will work, so examine your backyard carefully. For example, an area that receives full sun all day is ideal since plants can thrive under the warmth and sunlight.

Select the best spot with plenty of room between the pond and your home or any structure to allow plants and animals ample space to grow and move about. Make sure it’s protected from various elements such as wind and harsh weather conditions.

If you’re building a koi pond on your property, then the next question you have to ask is, “How big do you want your pond to be?” The good news is that the size of your pond can be as big or as small as you want it. It can accommodate any size koi, but choosing the right size is important so you don’t overstock your pond. Be sure to consider the size of your garden, where you’re placing your pond, and if you’re doing this alone or with a group of friends and family.

Dig Your Pond

After deciding where you want your pond in your landscape, it's time to dig the hole for your pond. In areas where freezing temperatures are only a concern in the wintertime, you can start your dig in the spring to allow at least several months for the enlarged trench to settle. It's usually smartest to hire a professional contractor to do the digging for you, especially if the ground is rocky, or if there are other factors like a shallow water table.

The two main considerations when digging your pond are how deep you want your pond, and how wide you want your pond. You generally want to dig your pond at least 3 feet deep, but you'll want to go a bit deeper in rocky or sandy regions. On the other hand, 2-four feet is usually more than enough depth for a pond, and you'll need to reduce the size of your pond if your property is limited in terms of width. Generally, the more width you have, the more water your pond can hold. Also, deeper ponds are usually more stable in terms of the water level.

Once the pond is dug, it should be allowed to settle for 4-6 weeks before the installation of a pond liner and any plants or fish.

Step Three: Place Equipment And Liner

Now that your oval-shaped hole is dug out, it's time to place your equipment inside of it. The equipment includes the pond liner, a pump, a skimmer basket, filtration equipment, and the decorative plantings (if you haven't already put those in).

These pieces should be placed in the hole in the following order (nothing dried):

  • The pond liner;
  • The decorative plantings;
  • The pump;
  • The skimmer basket;
  • The filter; and

The spigot.

The final piece of the puzzle is to fill the pond with water. Leave a couple of inches of water-free space at the top of the liner as well as at the bottom, so that you can easily pour water in each side. One side of the pond will be shorter than the other, because you left yourself more yard space on that side.

This water free space is where you'll put in your spigot. You won't be able to use the spigot until you level out the yard, so do this first.

Once your spigot is in place, you'll be left with about a 2-inch water-free spot at the top of the liner. This is where you'll want to set your skimmer basket.

Add Liner

Rocks, Plants, and Filtration.

Next, you need to decide how much space you want your pond to take up. If possible, work with the landscaping scheme in your yard so the pond blends more seamlessly into your outdoor design. You can choose to add a deck or simply leave the space unoccupied.

Lining the pond with a pond liner is recommended; it will prevent the ground beneath the pond from eroding away as the water level in the pond rises and falls in the hot and cold seasons.

Pond liner is a heavy duty material with a high mesh count that provides structural support and minimize the amount of silt in the pond. It comes in rolls that you lay under the ground surrounding the hole. Create the pool shape on the ground and cut the liner to fit.

Next, add some gravel or rocks before filling the hole with water. This way the liner will adhere to the ground.

Level the rocks in the liner. Gradually add water to the rocks to allow it to settle and contact the liner. After reaching the level of the ground, fill the pond with water and let the water adjust to the air temperature.

Step Four: Add Rocks

The third step, lining your pond with a layer of sand and a mixture of pea gravel and stones will help the construction process become a lot easier. You will need to pile the sand and gravel mixture to create a stone retaining wall around the perimeter of your pond. This is going to keep the water that is built up in your pond from trickling out. It will also prevent the sharp edges of rocks from puncturing the liner of your pond. Keep the rocks as close to the water as possible. According to LeptoSupply, you will need to add rocks that are 1/3 the size of the battery size in your pond. You can also use large river rocks if you prefer and another excellent choice is broken stones. Remember, the rocks should just be placed on top of the liner and installed about halfway up the liner. Simply plug in the battery with the pump now and you will have the force to fill in the rocks around the perimeter of the pond.

One of the most important parts of building a pond is the correct installation of your liner. Make sure it is not too loose or too tight and that it lies flat enough to make a seamless appearance. Making sure that your liner is properly situated is a crucial aspect of the pond building process that should not be overlooked. You should also make sure that there are no bumps or rips.

Start With Large Rocks

There are three steps to putting together the base of your backyard pond. First, choose the area where you want your Koi pond to be located. Then conduct a soil test to make sure that the soil does not consist of materials that will hurt the environment. You will also be able to use the test results to determine an area that would take the best natural filtration for your Koi pond.

It is hard to adjust the water level of an established pond, but if you are still in the planning stages, choosing a location that is easily accessed for maintenance and water-level changes is important. Water-level changes can be made by digging out of the middle of a pond or by installing a low lying area along the outer edges. The second step is determining the dimensions of the pond. Measure the width and length and install a depth-marker at the top and bottom of the pond to help determine volume and depth. Volume is very important when determining the strength of a Koi pond filtration and pump system. The last step is to remove vegetation from the pond site.

Dig a High Ridge

In the same way that you might build a barrier wall for a vegetable garden, the barrier pond wall and the dropoff provide two positive growth and pond management benefits. The barrier wall enables the pond to hold more water, and the pond can be built to a smaller footprint as the dropoff slopes dramatically toward the main body of the pond.

In the same way that you might dig a trench to improve drainage, a dropoff slope also improves water movement in the pond when water enters near the surface, and the water must go down to get across the pond. This rate of flow will be the largest possible because the water is moving much more slowly as it travels the longer distance.

You must remember that you are working with plumbing that leaks. Water that is trying to move downward leaks through the barrier wall and water that is trying to move upward leaks through the gate overflow. Finally, the same water trying to get into the pond down and the water trying to get out of the pond up will combine at the dropoff to make more water that leaks upward through the overflow and waterfall. All this leakage will tend to make things leaky. If your gate is leaking, you may need a new one.

Add Lighting

A light source will make your water easier to see in and will also help keep your pond at a cooler temperature. At night and in shaded areas, the water will become uneven, but adding a light will help create a more even temperature throughout the pond.

You may also find that a light could be used if you have fish that prefer dimmer conditions. Some koi fish like the cover of night for sleeping, but others like brighter conditions. A light allows you to create a variety of conditions. It is also a good idea to have lights on your pond if you live in a colder climate. Koi fish and other aquatic life really don't like the cold.

Although the motion sensors are a very convenient way to control lights in your koi pond, all of them are designed to turn off when the lighting is in direct contact with the water and your fish may not appreciate that.

When choosing a light for your pond, look for lights that have a durable water proof coating and that have a bulb that will not break in contact with water.

Step Five: Fill With Water

Once you have filled the pond and covered it with the pump and filter covers, put in a water heater.

The water should gradually heat up to a warm enough temperature that will help it to be hospitable to the fish you are going to place in the pond. The temperature should never be higher than 62 degrees Fahrenheit. The water heater should be in a location that will not flood your entire yard but will be far enough away from the pump and filter.

If you have added a fountain, it is a good idea to get some rocks you can use to secure it and contain it. Do not get rocks that were exposed to chemicals or concrete. You can purchase rocks at your local garden store; and if you need to build the rocks with cement and such, make sure it is a water-proof cement.

This cement will only be on the inside of the rocks and won’t stain the pond. Make sure to let the cement dry a bit before placing the water pump inside of it.

After you let the rocks dry, place them in the middle of the pond and secure them with cement.

The ideal water temperature for Koi is from 75 to 80 degrees Fahrenheit. Anything more or less will stunt the fish from growing to their potential.

Adjust the Water

The distinction between ponds and lakes is mainly a geographic one, but a pond is generally smaller than a lake and surrounded by land. A pond is also fed by a permanent water source (e.g., rain, underground springs, or a nearby creek or river).

There are multiple ways to excavate a pond, starting with digging a hole and continuing with waterproofing a pre-made liner to place in the hole, but it is often simply easier and more efficient to buy a pre-formed garden pond. Whether you buy a pre-made pond or dig your own, make sure to build the sides deep enough and wide enough to stop even the most determined frog from jumping out the other side.

Step Six: Install Equipment

Pump the water into a holding tank if you so choose. This may sound challenging, but the pump is placed one section from the filter. You will need to place a small hose into a hole next to the filter. You can use a bucket if you do not want to connect the hose to the filter. Use a hose clamp to secure the hose to the filter.

Install an air stone next to the pump. This will help control water circulation and add oxygen to the water. A good place is on top of the pump. You can use a clamp to hold the stone in place.

Place the bio filter into the bottom of the pump during construction. Do not forget to put the tubes into the tank and place both into the pump water chamber. Continue with the water chamber by sliding your lily pipes into the slots. Make sure they are secure throughout the hole.

Install the UV light if you so choose. This will help keep the African Dwarf Frog temperatures low, reducing stress on the animal. If you do not have a UV light, install rocks in the filter water instead.

Install the thermometer. Do not place the thermometer into the cleaning bucket. Use a suction cup or a clamp to place it on the glass.

Install a Filtration System

Water quality is extremely important in the successful operation of a koi pond. Filtration is a crucial factor to creating healthy water conditions that koi can thrive in.

You may find that your native streams and lakes contain substances that harm your koi. For example, a nearby creek may overflow with excessive rainfall, or even toxic sediment run-off from nearby areas. The filtration system filters out these impurities, so your koi tank remains clear and allows your fish to thrive.

A filtration system will also help you balance the pH and temperature of the water.

Ultraviolet filtration keeps waterborne parasites like Cryptocaryon out of your koi pond.

A UV filtration system doesn’t require an extra bag of salt to run it, and it is more practical than adding a chlorine filter for your koi pond.

Another bonus is that a UV filtration system helps with koi excitement. While the sunlight is not for they fish to bask in, it will help keep your fish healthy and your pond sparkling.

A proper filtration system is one of the most important components of a healthy pond. If you are going to invest in a koi pond, don’t skimp on the filtration.

Place the Aerator

The first piece of the koi pond puzzle is the aerator, also known as an “air pump.” It supplies oxygen to the water and makes your koi happy and healthy. Don’t put the air pump directly at the bottom of the pond – the koi will jump in and out of the water and won’t be able to get enough oxygen. Keep the aerator off to the side so the koi will swim underneath it to access the oxygen.

The correct amount of aeration is also important. Too much aeration can lead to oxygen depletion and can ultimately kill your fish. Check the label on the air pump to see how much aeration the pump provides per hour. The suggested level of oxygen for a koi pond is 3 to 5 parts per million. You can install an additional air pump if you need more oxygenation in deeper parts of the pond.

Place the aerator on the far side of the pond, out of the way of the koi. Also, put your new pump on a timer to match the times of the day and night when the natural aeration happens. It will ensure your koi always have enough oxygen in their pond.

Step Seven: Add Plants

Now that you have a pond, you can add plants, rocks and other decorations to make your koi pond look gorgeous and give some shady areas to escape the scorching summer sun. Koi prefer to hang out under the shade with lightly flowing water for a break from the heat. To add plants to your pond, add a mesh cover over the drainpipes and fill them with water to float the plants.

The mesh covers will filter out the dirt and leaves from the water and allow sunlight to penetrate to the bottom for pond plants to grow. Suitable plants for the koi pond are water lilies, lotus, hyacinth, iris, duckweed and other aquatic plants. Lotus and water lilies require more maintenance as they tend to rot, so make sure to change the water in the mesh covers often.

Choosing Your Plants

Once you've decided on the plants you want to use, it's time to create your layout. Decide where you want each plant to grow and how exactly you'd like your pond to look. Take into account how tall your plants are, and where you want the light to be in the pond. You also need to take to account how much shade your plants will need.

The shade effect of plants applies more to water lily than any other type of plant because they grow a foot or more above the surface of the water. When deciding on your layout, decide which plants will receive the most sunlight and which will receive the least. Keep in mind that plants need sunlight to grow strong underwater roots and therefore will do best in areas that receive sufficient sunlight.

The plants you fill your pond with will look off-center in the beginning, but soon your plants will create a natural flow in the design. You will also have more surface area for sunlight to hit the plants once you add water. This sunlight will feed the plants and help them grow and thrive.

When to Add Plants

In general, aquatic plants are the plants of choice for koi pond construction. Koi prefer to be in a shallow environment with an abundance of water plants. They need cover and needs different temperatures that a koi pond provides. Planting the koi pond properly is essential to a healthy koi pond.

For the most part, you should plant koi pond plants in your koi pond after your koi are moved into the pond. Before the koi arrive, you can often add annuals. Annuals are plants that live for only one year and then they die.

Use large amounts of annuals to create a small jungle for the koi to explore and enjoy.

It is possible, though more difficult, to plant aquatic plants in your pond before you have your fish. You should do this early in the season, before your plants flower. Koi ponds are not shallow ponds and this means you need to have plants that can survive in the deep portions of your koi pond.

In these deep sections, plants need to be able to survive in low-light conditions, too. This will make it easier to keep the plants since they are going to need deeper water.

Step Eight: Add Fish

And Plants and Admire.

It’s important to know that you must wait about one month before adding plants or fish to the koi pond. Koi may seem to be fine for 24 hours after being added to their new home, but adding plants and fish before this month of settling in is dangerous for fish and new plants. It's best to wait on the fish and plants until the one month mark.

A four inch layer of gravel is good enough for now. In the future, you may want to cover the entire bottom of the pond with additional gravel to keep the water cleaner. A bad water filtration system will be a constant drain on your wallet. You should invest in a good filtration system. If necessary, you can have a water test performed every couple of months to check for dissolved oxygen and pH balance.

A good Koi pond is as healthy as the fish and plants. The more plants and fish you put in your koi pond, the healthier it will be. If you already have koi, make sure you bring them along with you when you move your koi. Be sure and prepare your fish for their new environment. You can do this by gradually introducing your fish to their new environment. Slowly increasing the water column in your new home with a little water from your old home will do the trick.

Best Fish For Your Koi Pond

Before you decide what fish to put in your koi pond, it is best to understand why koi have continually been a favorite as a landscape addition. Koi are ornamental fish that add color to your backyard. They require little maintenance and they are very interesting to watch. Koi are good pond fish for beginners.

Koi are available in a variety of colors. They come in shimmering metallic greens and reds, and even tobacco and gold colors. They can live for many years and grow to a large size. Koi can become dormant during the winter, or they can survive outdoors year-round in warmer climates.

Koi can be quite expensive, so be sure to know how much you want to spend before bringing them into your pond. You may be more inclined to add fish if you are aware of what each fish will cost. You may also want to try to save money by scouting out aquariums and fish tanks that are being sold. This can save you money and provide you with attractive, healthy fish.

As your pond fish grow, it is best to avoid introducing smaller fish to your pond. Koi can develop a taste for other fish and will eat them. The only exception to this rule is if the new fish is a male. The male is able to intimidate and chase off any other fish that sleep near his nest.

Step Nine: Koi Pond Maintenance

One aspect that is often overlooked in a koi pond is the pond bottom. Pond bottom is a very important area and should not be ignored. Minus food and wastes from the fish, the majority of the waste products that are in the pond come from the water that settles in the bottom.

Since the bottom of the pond is not constantly stirred up by the filter system, the layer of mulm tends to build up. A thick layer of poop and mulm is a perfect home for all sorts of bacteria and bugs, one of which is the dreaded amoeba that can cause your fish to become very sick and possibly even kill them.

Pond Bottom Maintenance

{1}. Clean out the pond for a complete cleaning before the winter season.
{2}. If you have plants in the pond they will need to be removed. Most plants will not survive the transfer to another pond and those that do eventually go into shock(usually caused by an ammonia build up) and die.
{3}. Skim as much of the mulm out as you can with a net and vacuum, leaving no trace behind.
{4}. You can add your favorite pond plants back into the pond to re-establish the biological filter and provide both a biological and scenic element to the pond.

Feeding Fish

Fish fed regularly, just enough, and the right kind of food, are healthy fish that will live a long time. Overfeeding your fish will kill them just as surely as starving them to death. There are two key ingredients to feeding fish correctly:

Just enough food.

The right kind of food.

The first rule will be your guide to over-feeding and the second rule will help you avoid under-feeding. The fish feed scale is a fishing scale with an in-line hose and a timer, trip switch, or manual shut-off valve.

Add as much as you want and the scale takes care of the amounts and the time.

The right amount is the amount of food that the fish will eat in ten minutes. If they are unable to eat it all in ten minutes you are feeding them too much. If it is still there in ten minutes, you are not feeding them enough.

A better indicator of how much to feed is how much the fish are eating. A properly fed fish consistently consumes all of the food you give it. If the fish are only consuming part of their food, then you are not feeding them enough. Likewise, if they are gulping down all of their food in a few minutes, then you are feeding them too much.

Monitor the amount of food you feed and make sure that you are feeding your fish just enough and no more.

Don’t Let the Pond Get Crowded

The basics of koi pond hobby are very easy to understand. There are a few simple things to keep in mind when you’re building your pond, though. Allowing your pond to get too crowded by koi can be potentially dangerous. You will have to keep your pond in a well-maintained shape. Without proper maintenance, your koi can get sick or injured and they won’t grow to be healthy. Also, if you don’t keep the water clean, your koi are likely to contract diseases and become very weak.

Aquascaping is a creative way to build your koi pond and it only needs some basic tools and materials that you may already have. If you’re planning to construct your own koi pond, follow our tips below and DIY!

Perform a survey of your property and choose a location that has the best possible exposure to sunlight. You don’t want shaded areas in your koi pond, because they can create algae growth.

Make sure to find the best source of water for your koi pond. If you’re planning to build a pond from scratch, you will need a pump to keep the water circulation.

Clean Your Pond Regularly

The actual concept of how to build a koi pond is relatively simple. The thing many people do not think about, is the time it takes to care for your koi pond after it is built.

The first few months following the construction of the koi pond will determine if you love your new feature or if you will be moving it to the back yard.

If you are able to plan a vacation for a few weeks after the pond is built, this will allow you to relax and enjoy your vacation, knowing your pond is being properly maintained.

Completely clean the pond out each, at least, once a month, since for the first few months until the pond gets established it is very important to do this. Once the koi population is established and the pond is thriving, it will be easiest to manage all other maintenance with a deep or intensive cleaning once every three months.

Some backyard pond owners even do a partial cleaning each week, so they are sure to not miss anything at important times such as, just after the koi spawn.

Pond cleaners are available at any pond supply shop and a shallow skimmer type, poked in the bottom of the pond with a twig can be used to skim the very top layer of the pond.

Get the Right Equipment

Before you begin building your koi pond, you must be aware of the equipment you may need to build and stock the pond. This includes getting a pump and pond liner, and depending on the size, setting up a water treatment system and filters too. You will also need a solar cover to keep temperatures down in the summer.

Next, you should consider a taiwanese ink stone to help purify the water of dissolved solids. You can also get a UV light to add to the koi pond to help prevent and remove fungal infections. A substrate and protective covering is needed to keep the fish healthier. A koi pond heater and a proper filter will help maintain healthy water temperatures for the fish.

The koi pond chemicals you choose to add the water must be non-toxic to the fish. Try to avoid copper as a chemical treatment as this can harm the fish. Instead, search for other options like water treatments that use a bacteria to treat your water.

Finally, you must plan on a temperature gauge and water testing kits to ensure your pond is healthy.

First you must decide which fish you want. Most koi pond owners choose carp as their fish of choice. If you are not familiar with caring for them, you might want to choose other species of fish. You must also consider what type of habitat you have, to help create the right koi pond.

Keep Pond Safe From Predators

Fences, fish nets, and electric shockers keep predators out of the pond, but these measures are expensive and can be burdensome. The best way to keep predator animals out of a koi pond is to conceal the pond from predators, which makes it harder for them to find the pond in the first place.

The fish in your pond can sense danger and they will have a heightened sense of awareness if the pond is obstructed, so concealment is not just a matter of protecting them from predators but also protecting them from the stress of being visible to predators.


Have a spillway (small waterfall) for excess water to exit the pond.

Maintain no fish that will offend the wildlife (such as koi and goldfish).

Have a skimmer to remove trash from the surface, which can draw predators.

Make the pond difficult to reach by building it into the ground or in an area with thick foliage.

Maintain a natural environment around the pond to encourage wildlife to use the pond as a natural water source.

Provide healthy water and cleanliness. Predators are less likely to go near an unhealthy-looking, stagnant pond.


Build the pond if flooding is a possibility.

Allow overgrowth of aquatic weeds or algae which can lead to water stagnation, negative health effects on fish, and can become a food source for predators.

Final Thoughts

You can reach the point when you simply cannot have any more fish in your current koi pond. They have outgrown the capacity of the pond and you really want to take care of them.

If you have had koi in your pond for some time, you really want to make sure that you have plenty of room for them.

Overcrowding koi is something that you do not want to do. It is not good for the koi that are in the pond. It can also lead to disease issues as well.

If you have a family and want to make sure that your children are safe and that you are safe as well, you will need to make sure that you have plenty of extra space, in your koi pond.

Have you ever had your children visit your koi pond? They may think that it is simply a space for them to have fun. However, they do not realize that there are fish in the pond. This may lead to them doing things in the pond that you would not want them to do. This can be a safety hazard for them and for the fish as well.