If you have a koi pond, you may have noticed dead fish sometimes appear after it rains. This can be a frustrating and perplexing problem, but there are a few reasons why this happens.
In this blog post, weâll explore some of the reasons why heavy rains can cause koi fish to die and offer tips on how to protect your koi fish from the effects of rain. Knowing this will help you know how to better care for your koi fish.
Why Are My Koi Fish Dying After It Rains?
Heavy rains can be disastrous for your koi fish pond. Many koi pond owners have woken up after a heavy rainstorm to find that most of their fish have mysteriously died. While itâs not always clear why this happens, there are several possible causes that koi fish experts have identified.
Why Heavy Rains Can Cause Pond Fish To Die
Here are 4 of the main reasons why dead fish appear after it rains.
Torrential Rains Cause Turnover
One possible answer to the question, âWhy are my koi fish dying after it rains?â is that it results from turnover.
Turnover: Turnover happens when heavy rain stirs up the deeper layers of oxygen-depleted pond water. When this occurs, the low-oxygen water typically at the pondâs bottom rises to the surface. Since fish are usually found near the surface, turnover can suddenly immerse your koi fish in low-oxygen water, causing them to literally suffocate.
Temperature changes: Besides surrounding your koi fish with low-oxygen water, torrential rains can also change the pond waterâs temperature. This can be deadly for koi fish because they are cold-blooded animals that rely on the temperature of the water to regulate their body temperature.Â
So if youâre wondering, âwhy are my koi fish dying after it rains,â it may be something as simple as a drastic temperature swing.
Cloudy water: Heavy rains not only stir up low-oxygen water from the bottom of the pond, but they can also stir up sediment. Sediment can cause the pond water to become cloudy, which can also stress your fish.
Heavy Rainfall Causes Surface Runoff
Surface runoff is when rainwater runs over the ground and picks up pollutants like fertilizers, pesticides, and other chemicals before it flows into your pond.
These pollutants can be deadly to your koi fish and will kill them if they accumulate in sufficient amounts. Surface runoff can also change the pH of the pond water and make it toxic for your koi fish. Most koi fish prefer a pH between 7 and 8, so anything drastically outside that range can be deadly.
Rainwater Can Change Water Chemistry
Unfortunately, after it rains, there can be a significant change in water chemistry which can be deadly for your koi fish. Rainwater is typically full of nutrients that are beneficial to plants, such as nitrates and phosphates.
However, too much rainfall can overwhelm a pondâs ecosystem and its ability to filter the sudden influx of nutrients. When this happens, these normally beneficial nutrients can cause an increase in algae growth and depleted oxygen levels, leading to death.
Another possible answer to the question, âwhy are my koi fish dying after it rainsâ is related to the pH of the water. Rainwater can also be slightly acidic or alkaline, which will disrupt the pH necessary for healthy koi fish. If you live in an area with heavy pollution, acid rain could also drastically alter the pH levels of your koi pond.
 Flooding Can Wash Away Koi Fish
A torrential downpour can physically wash away the fish and even their eggs, which spells certain death for them. If you see your koi fish beached on the edge of your pond after heavy rainfall, you might be able to save them by simply returning them to the pond water.
How To Protect Your Koi Fish From The Effects Of Rain
Now that you know the answer to the question, âwhy are my koi fish dying after it rains,â letâs take a look at how to protect your koi fish from the harmful effects of excessive rain.
Increase Aeration
Aeration helps increase dissolved oxygen levels in the water, which helps keep fish healthy and happy even during heavy rainfall. To protect your koi fish from the effects of turnover due to heavy rainfall, you should start increasing aeration in your pond using a bubbler or an aerator.
Maintain Proper Balance Of Pond Plants
One solution to the question, âwhy are my koi fish dying after it rainsâ involves plants. Aquatic plants help to absorb excess nutrients and reduce algae growth. They also help to filter out pollutants and provide dissolved oxygen for your pond fish to breathe.Â
Pond plants can also function as a physical barrier against heavy downpours and prevent washed-in pollutants or foreign objects like leaves, plastic bags, or dead insects from creating further imbalance in the ecosystem.Â
On the other hand, you donât want to overcrowd your pond with too many plants since that can reduce the available water surface space for your pond fish.
Build Up Edge Of Pond To Prevent Surface Runoff
To prevent surface runoff from entering your pond, you can build up the edge of your pond with an earthen berm (a wall of dirt extending around the perimeter). This helps deflect surface water away from your koi fish habitat, keeping them safe from downstream pollutants.
Be Vigilant With Maintaining Correct Water Chemistry
âWhy are my koi fish dying after it rains,â is a common question asked by pond owners who fail to maintain the correct water quality for their ponds. A disruption in the pondâs water chemistry can quickly turn deadly for koi fish.
To prevent this, itâs important to test and adjust the pH level, hardness, and other measurements frequently, especially after large storms. If youâve had sudden and dramatic changes in these parameters, you may need to add buffers or chemicals to restore balance in your pond. Â
Install Bog Filter To Minimize Pollution
Bog filters are natural filtration systems that use plants to reduce the levels of pollutants entering your pond. These filtration systems work by trapping debris and extracting nitrogen from the water, mitigating excess nutrients caused by torrential rain.
Limit Use Of Fertilizers Near Your Pond
As the old saying goes, âAn ounce of prevention is better than a pound of cure.â One way to mitigate the harm of surface runoff caused by heavy rain is to limit the use of chemical fertilizers near your pond. It is essential not to overfertilize your lawn, as this will guarantee heavy runoff in the event of rainfall.Â
Promptly Clean Any Debris
Promptly cleaning up any debris around your pond is a good way to avoid ever asking the question, âwhy are my koi fish dying after it rains?â Regularly and promptly removing any debris around your pond will prevent it from washing into the pond in the event of a downpour. Organic debris such as grass clippings, as well as trash, can degrade the water quality to the point that it will harm, or kill, your fish.
Use Adequate Filtration Systems
If you are already not using adequate filtration for your koi pond, heavy rainfall that introduces even more pollutants will quickly overwhelm your filtration system. This is why itâs important to use a high-powered filtration system that will effectively filter out any debris and contaminants and maintain the water quality for your fish.
Besides debris removal, these systems also help to reduce stress on the koi fish by removing oxygen-depleting ammonia and other compounds that are introduced into the water as a result of rainfall.Â
Install Overflow Drain To Prevent Fish From Washing Away
One way to prevent your fish from washing away is to install an overflow drain at a low point near your pond. This will allow the excess water from any heavy rainfall to drain away rather than overflowing your pond.
Redirect Water Flow Around Your Pond
As noted above, one possible answer to the question, âwhy are my koi fish dying after it rainsâ involves surface runoff accumulating toxins in your pond. One way to avoid this is to have a plan for proper water management and flow around your pond before heavy rains arrive.
Start by reducing any standing water near your pond with redirecting channels or simple grading. This will provide an outflow alternative for the extra water that accumulates on your land during storms.
Use Fencing To Help Keep Fish In Your Pond
Sometimes the answer to the question, âwhy are my koi fish dying after it rainsâ is that the fish were simply washed out of the pond.
Installing temporary fencing, netting, or other types of barriers around your pond will keep your koi fish from washing out of your pond. Since most people do not want fencing detracting from the natural appearance of their pond, this solution is probably best used as a stop-gap measure until a more permanent solution is implemented.
Charlotte Backyard Ponds Can Repair And Renovate Your Koi Fish Pond
Now you know the answer to the question, âwhy are my koi fish dying after it rains?â Fortunately, with a little bit of preparation, you can ensure that your koi fish are safe and sound even during the heaviest rains.
If you have further questions or need assistance preparing your pond for rain, donât hesitate to reach out to us. We would be more than happy to help you protect your fish friends. Fill out our contact form today, and one of our experts will get back to you as soon as possible.