How to get rid of duckweed? Let’s find out!

Common duckweed, whose scientific name is Lemna minor, is a quickly spreading aquatic plant. In large numbers, it deprives ponds of oxygen, thereby resulting in the death of beneficial algae and fish in still waters. To preserve your pond and the existing aquatic life in it, it is important to get rid of duckweed. This article shows you how!

controlling duckweed

Table of Contents

How to get rid of duckweed?

Well, prevention is the safest and most effective way to get rid of duckweed from your pond. It’s always best to consider using natural ways to do the job; however, if the duckweed infestation is beyond control, you can go for chemical treatments. Some of the most popular methods to control duckweed in ponds include nutrient reduction, bubble aeration, and physical removal. Before I get into the details, it’s important to know some facts about duckweed. Let’s take a look at it.

nutrient rich ponds

What exactly is duckweed? How does it affect a water body?

Duckweed is a vibrant green, free-floating weed often found in ponds or slowly moving water bodies. The build-up of its leaves on the pond’s bottom creates stratification. Duckweed is an invasive and nuisance weed that occupies older ponds and quiet, undisturbed water bodies.

A smaller plant named watermeal often accompanies duckweed. Both of these work together and rapidly cover susceptible ponds when conditions are ideal for their growth. Duckweed control must start early in the spring. If left unnoticed in the beginning, it may even take years to successfully get rid of duckweed in ponds.

Biologically speaking, duckweed spreads quickly over the pond’s surface. It decreases the oxygen level in the pond, thereby affecting the lives of fish and desirable aquatic plants. The higher the nutrient level of the pond, the more challenging it is to control duckweed. Animal and agricultural lot runoff, geese, leaking septic tanks, and lawn fertilizers are some of the sources that contribute to excessive nutrient levels.

Water bodies that are naturally in motion or moving tend to have fewer issues and hence require less duckweed control.


Is it mandatory to remove duckweed from your pond?

While it’s crucial to get rid of duckweed, small amounts may often be beneficial, because they offer some benefits: reducing excess nutrients, improving oxygen levels, controlling algae growth, and providing predator and shade protection. 

However, the issue with duckweed is that it could be difficult to maintain. Moreover, if the water body is already rich in nutrients or has issues with water quality, duckweed can easily spread at lightning speed.

You can remove duckweed if you hate its look on your pond or if it’s growing and spreading too fast, causing problems with water conditions. When there are fish in the pond, excess duckweed can quickly reduce oxygen levels and increase ammonia.

In contrast, if there aren’t any fish in the pond, retaining duckweed is actually more of a personal choice, because it doesn’t cause any major problems with the ecosystem. Also, if there are plants like water lilies, these can also suffer, because duckweed takes a share of their nutrients. So, you should think along these lines when you’re considering the removal of duckweed.

waterlily pond

Preventive measures to control duckweed

If you’re choosing to get rid of duckweed, as mentioned earlier, prevention is the key. Don’t forget that a single small duckweed plant is capable of forming a population. So, exercise caution, especially when you buy new aquatic plants for your pond.

Only in-vitro plants are free from duckweed. In all other forms of cultivation, it’s not possible to completely exclude duckweed from the plants. So, when you buy plants from a nursery or get them from a hobbyist, make sure you inspect the plants completely before planting. Remember to rinse them properly under running water to get rid of any duckweed.

During the initial days after you set up a pond or a new tank, you should scan the water surface regularly. If you find any emerging pieces of duckweed, you’ve got to remove them immediately.

7 effective steps to get rid of duckweed

It’s true that duckweed plants can often be a nuisance if there is a pond or large tank on your property. The seed-bearing weed grows in colonies in calm water. It is very aggressive and can take over the entire body of water too quickly. If you want to ensure that this weed doesn’t take over your pond, the following tips and tricks can help.

1. Add natural duckweed predators

Adding natural predators to the pond and the area surrounding it is a great way to control duckweed. A few popular predators that love to eat duckweed include goldfish, koi, and grass carp. While these fish cannot get rid of a massive duckweed problem, they’ll ensure that the duckweed population doesn’t become larger. Domesticated waterfowl such as geese are also natural duckweed predators you can give a try.

However, you’ve got to make sure that waterfowl doesn’t carry the seeds to the nearby water bodies and spread the weed. You can use natural duckweed predators to control a small population of duckweed in your pond.

2. Manual DIY removal of duckweed

While this is not the easiest option, it’s the best way to get rid of most duckweed from your pond, especially if there are fish. Removing duckweed manually using a vacuum cleaner or strong net is a good choice.

Duckweed is not like algae, which normally comes in many forms and hides throughout the pond. Duckweed will be clearly visible, making it effortless to net out. Moreover, you gain full control over cleaning. You can also choose to leave a little duckweed behind if you wish to keep the positive aspects that come with the presence of a small population of duckweed plants.

Manual cleaning works best for small ponds, however, it also works fine for larger ponds, especially if you can monitor the water quality and keep it in check. If the water quality is good, duckweed will not grow too fast, which demands constant clean-ups. If you test the water quality beforehand and simultaneously enhance the conditions manually by removing duckweed, you can easily control the weed as well as promote safe fishkeeping.

If you’re facing a small duckweed problem, you can use a good-quality net to clean out the weeds. Once you’ve removed the majority of the visible duckweed, try using a natural duckweed killer to ensure that the maximum number of duckweeds are removed.

3. Aerate the water

Duckweed thrives in stagnant or slow-moving water. To eradicate duckweed from your pond, you can aerate it. Use bubble aeration to discourage duckweed growth and kill duckweed plants that are already established. Another benefit of aerating a pond is that it reduces foul odors associated with the water.

4. Rake the water

You can use a rake to physically remove duckweed from the surface of the pond. All you need to do is simply rake all the leaves together and get rid of them from the water’s surface. Make sure you dispose of the plant quite far away, especially from any water source. This prevents the weed from getting back into the water through wind, runoff, or animals. If you don’t prefer raking duckweed by hand, you can use a vacuum to get rid of duckweed from the pond’s surface.

5. Reduce fish feeding

If there are fish like goldfish or koi in your pond, try bringing down their feed doses, so that you encourage them to feed more on duckweed. These fish love to feed on duckweed. You can see that many ponds with a lot of fish never have issues with duckweed, because the fish eat the weeds as they grow. You can use this method if there is only a small population of duckweed in your pond.

feeding fish in pond

6. Prevent waterfowl access

While waterfowl like geese might add to the look of your pond. They can worsen a duckweed problem significantly. Waterfowl feed on duckweed; in other words, they often have some of the plant stuck to their beaks, feet, and feathers, thereby easily spreading the weed.

You can control waterfowl access by making your water body less attractive to these birds. Consider forming a steep bank in the pond, using noise-making devices to frighten them, and removing aquatic vegetation.

7. Use safe chemicals

If none of the above methods worked for you due to a large colony of duckweed, safe chemical options are a good bet. Choose an herbicide that contains fluoridone. Diquat dibromide is another herbicide that helps control duckweed. Another safe chemical to effectively get rid of duckweed is flumioxazin, which is a fast-acting herbicide. You can use it to effectively remove young, actively growing duckweed plants from your pond.


How to get rid of duckweed? I’m sure this article has provided you with all the information you need with regard to this question. Let’s do a quick recap of the important points:

  • Duckweed is a fast-growing, floating weed found in stagnant or slow-moving water bodies.
  • Prevention is the key to stopping the spread of duckweed. You should manually remove any duckweed plants the moment you notice one.
  • To get rid of a large duckweed infestation, you can try several methods, including adding natural predators, bubble aeration, reducing fish feeds, preventing waterfowl access, and using safe chemicals.
  • It’s important to note that a small amount of duckweed is harmless, but if you find them unsightly, it’s up to you to remove them according to your preferences.
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Oliver Wright
Oliver Wright

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