Do Garden Ponds Overflow When It Rains?

Undoubtedly, my garden pond is my favorite spot, since it attracts birds, dragonflies, and butterflies. It is also the central feature of our landscape. When we chose the spot for the pond, we considered everything, including the cost, size, and location, but overlooked heavy rainfall.

Garden ponds overflow when it rains heavily or if it rains for a long time. The size and design of the pond also determine if it will overflow. If you install overflow pipes redirecting excess water to a water storage tank or garden area, you can prevent this.

I’ll discuss garden ponds in detail, when they overflow, and what you can do to keep your garden pond from overflowing.

How Rain Affects Garden Ponds

Garden ponds do much more than improve the aesthetic appeal of your landscape. They also support life, both plants and animals. Rain is not a problem if you only have light showers. However, you may have reason to be concerned if you experience heavy or prolonged rainfall without an overflow system.

The Garden Pond Will Overflow

The immediate effect of heavy rain on the garden pond is it will fill up and eventually overflow. Sometimes the overflow is partially because of the rain, but also the position of the garden pond.

Ponds in low-lying areas tend to collect water from the garden on higher ground. 

Rain accompanied by high winds may also cause garden ponds to flood when a lot of water is forced to fall in the direction of the pond. If the rains are heavy and the winds strong, your garden pond is at risk of overflowing. 

Rain Changes the Pond’s Chemical Composition

Rain contains several components, such as: 

  • Phosphorus 
  • Magnesium
  • Calcium
  • Nitrogen
  • Sodium

This is primarily because of the rainfall cycle, which includes nutrients from the soil, plants, and the atmosphere. 

While water is very beneficial to plants, when heavy rains cause the garden pond to overflow, these nutrients can overwhelm the garden pond and the life inside it. 

For example, nutrient abundance will feed harmful algae, causing them to grow significantly. Besides the nutrients in the rain, some nutrients may be from runoff water from the fertilized garden and lawn. 

Algae compete with fish and other plants for oxygen; if allowed to grow, the algae usually win. 

Additionally, these nutrients combined with pollutants (nitrogen dioxide and nitrogen oxides) make the rain highly acidic, with a pH of 5.0 – 5.5. However, the concentration of these pollutants makes the rain more acidic. 

The ideal pH for pond water for fish is 6.5 – 8.5. Fish blood has an average pH of 7.4, so the pond should have a pH as close to this as possible. 

When the rain is released into the pond too quickly and within a short time, it changes the pond water’s pH. This explains why some people complain that their fish die after it rains

When the pond water pH changes suddenly, the fish will lose the protective mucus on the gills. This exposes the fish to numerous pathogens, making them vulnerable to parasites and illnesses. 

Rains Causes Water Turnover

During the warm season, the oxygen-rich water is usually closer to the surface of the garden pond. Cold water is denser than warm water, and it also has less oxygen, so it is found at the base of the pond during summer. 

However, dense, cold water is dumped into the garden pond when it rains heavily. This water quickly settles at the bottom and, in turn, displaces the low-oxygen water, causing it to move to the top. 

The water turnover and change in water temperature suddenly expose the fish closer to the surface to low-oxygen water, causing them to suffocate.  

The Overflowing Garden Pond Will Wash the Fish Out

The other immediate effect of an overflowing garden is that an overflow will wash the fish out of the pond altogether. As the water flows out of the pond, the fish may go with it.

If you’re home, you can save the fish by putting them in tanks or containers and transferring them indoors. You may find dead fish scattered in your garden if you aren’t at home.

How To Keep the Garden Pond From Overflowing

Since you cannot control the rain, you should find ways to keep your garden pond from overflowing. Even if you don’t keep fish, an overflowing garden pond is an eyesore and can ruin the plants and waterlog the soil around your pond.

Install an Overflow Pipe

You can install an overflow pipe vertically or horizontally, depending on the position of the pond and your intentions with the excess water. Once the water reaches a set level, the overflow pipe will drain the excess water away.

The best time to install an overflow outlet is when constructing the pond. However, you can still do it later on an established pond. The overflow pipe should have a diameter of at least 2 inches (5.08 cm) and at least 10 inches (25.4 cm) long or longer. 

Ensure you position the overflow pipe correctly above the natural water level. If you place the overflow pipe too low, your pond will leak water, which will be a problem, especially if you keep fish. 

You should also ensure you have netting on the overflow pipe to keep small fish and debris from flowing through the pipe. This will also prevent clogging, which will cause the pond to overflow in case you have heavy rains. 

The AlpineReach Pond Netting Kit (available on is a heavy-duty mesh. It is strong enough to keep fish from flowing through the overflow pipe. It also prevents leaves and other debris from clogging the pipe. It is very versatile and easy to set up. 

Besides working as a barrier on the overflow pipe, you can use the netting to cover your pond to keep the fish from jumping out when the rains cause the pond to overflow. 

This YouTube video shows a pond overflow setup and how you can redirect and reuse the excess water:

Incorporate a Slope on One Side of the Pond

When building your garden pond, you should consider having a slope on one side. If you have fish, you can create a barrier that will allow water out but keep your fish inside the pond. This will help to avoid pond overflow during the rainy season. 

Build the Pond on a Higher Ground

Although the garden pond is often a central feature of the landscape, it needs to be in the best location. Even if another spot seems more ideal, you should avoid it if your pond is at risk of overflowing. 

Having a pond on higher ground is best because there is no risk of runoff water finding its way into the pond, causing it to overflow. 

What To Do When Your Pond Overflows

When you set up your garden pond in the ideal location and install an overflow outlet, you probably have nothing to worry about when it rains heavily. However, if your pond is overflowing, you’ll need to eliminate the excess water.

You can do this faster by pumping the water out. However, you’ll still need a drainage pipe to release the excess water. You can a submersible water pump to get rid of the excess water from the pond.

It is easy to use and has three outlets with different diameters, allowing you to remove water at your preferred pace. It also has an automatic on/off mode. When the float switch is on, it will pump out water until the water is below the pump, then it disconnects automatically.

Garden ponds can be hard to maintain. This is why I wrote this helpful article on whether maintaining garden ponds is hard, how to maintain a pond, and essential tips to remember. Don’t miss it: Are Garden Ponds Hard To Maintain?


If you have decided to have a garden pond, you must plan for heavy rains and pond overflow. An overflow pipe and a great pond design will keep you from worrying about pond overflow. 

You should also ensure you redirect the excess water to the garden using a garden horse. You can also drain the water to a storage tank.

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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