5 Reasons Why Your Pond Smells Fishy

From backyard ponds stocked with bass and bluegill to decorative koi gardens, there is just something soothing about being near the water.

However, sometimes our relaxing water retreats can smell a little fishy…and why is that?

In this article, ill discuss 5 reasons why your pond smells fishy, and give you some tips on how to get rid of that smell.

Algae Blooms

One of the most common culprits of a smelly pond is an overgrowth of algae, especially when it is blooming.

Many species of algae will produce by-products that will stink or release different tastes into the water. Because they are also living creatures, they can also produce plenty of smelly odors once they die off and start to decompose.

This can also result in a chemical imbalance that can potentially hurt the entire pond’s ecosystem.

Even though some algae is good for the pond and acts as a natural filtration system to break down organic waste, it will also dispose of all of the oxygen from the pond and could kill your fish.

Low Oxygen Levels

Speaking of low oxygen levels, this is another reason that a pond can begin to smell super “fishy”.

This is often due to improper water filtration from either the algae or other filtration systems.

Properly filtering the pond water will remove the organic and inorganic waste (which can also lead to bad smells). If the water is not properly filtered, the oxygen levels will slowly begin to drop.

Of course, low oxygen levels could also be the result of big algae blooms as we previously mentioned.

Whether the low oxygen levels come from the algae or improper filtration, it is bad news for your fish and can easily start to harm them.

The Fish Are Spawning

Fish populations will not cause a pond to smell “fishy” unless they are spawning.

When the fish spawn, they release eggs and sperm as well as other liquids that will produce a distinct fishy smell.

5 Reasons Why Your Pond Smells Fishy

While this is only temporary and should go away after the spawn, this is often the first thing that people will blame when it comes to a smelly pond.

After the spawn ends, this temporary rise in smell should dissipate shortly after as well. If the smell still persists, then you likely have other problems that are the culprit.

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Water Stagnation

Poor water movement in a pond can do many things such as reduce its oxygen supply, grow more algae, and produce odorous bacteria.

With stagnant water, you may start to notice many different smells from rotten eggs to that familiar “fishy” odor.

Once this bacteria starts to break down at the bottom of the pond, it will then begin to create carbon dioxide and hydrogen sulfide.

Both of these can produce terrible smells as well and can throw off the entire chemistry of the pond water.

Bottom Muck

As time passes, debris and waste will start to collect and decompose on the bottom of the pond.

All of this organic material can be made of everything from dead fish, chemical run-off, and plant debris.

While a small amount of muck and sludge is normal to have at the bottom of a pond, excess amounts will produce a strong “fishy” smell in a relatively short amount of time. And it can really get bad during the summer!

It is a good idea to keep an eye on the amount of black muck at the bottom of your pond in order to avoid it becoming a problem in the future.

How to Get Rid of Fishy Smell in Ponds

Once you determine what the root cause of the smell is in your pond, you can now get to work starting to fix it.

If the reason your pond smells fishy is because of the spawn, then all you will have to do is wait for it to be over.

If you have one of the other problems, however, it will most likely take a little bit of work in order to solve.

The first step is to check on your water movement. As we mentioned, stagnant water can cause a multitude of problems in addition to bad odors.

Does your pond have any drainage areas like culverts, creeks, or canals?

If you notice that you are not getting any water movement, you may need some aeration.

This will provide oxygen for the fish and good bacteria, nutrients for the plants, and keep substances from building up on the bottom.

Aeration can be achieved with a simple pump or fountain. depending on the size of your pond.

If your water is not stagnant and you notice other issues with your pond and its smells, you will then need to focus on cleaning and optimizing your filtration.

If your pond has a filtration system, make sure that it is working properly and is being maintained.

If you have a natural pond, you will need plenty of good pond plants to act as your filtration system. Contact your local fisheries biologist or county extension office to ask about native aquatic plants in your area.

Next, you will need to address the bottom muck.

With a smaller pond, you can use something like a pond net in order to remove excess sludge and clean up all of the filth.

For bigger ponds, you may need to use natural sludge breakdown chemicals in order to cover large areas.

In worst-case scenarios, it may be necessary to completely drain the pond and manually remove the muck.

Adding good bacteria and enzyme-based muck breakdown products will help to keep the muck at the bottom from producing hazardous chemicals and odors.

When it comes to introducing chemicals and controlling the pH, always consult with a professional.


Creating your own pond and stocking it with fish is a wonderful hobby. You get to control your own micro-environment and watch your prized fish grow.

But it does not come without challenges. Pond and lake ownership is a big responsibility!

I always recommend consulting with a pond or lake management consultant and checking with your local state guidelines.

See Also: Pond Fishing Boats…Which Style Is Best For You?

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