What is Duckweed?

Mary McMahon
Mary McMahon

Duckweed is a free-floating aquatic plant that grows in both still and running freshwater, such as lakes, rivers, and streams. Contrary to what one might expect from the name, no ducks are involved in the growth habits of the plant, although ducks undoubtedly feed on it when they find it growing. Depending on the circumstances, duckweed can be an extremely invasive species, or a welcomed aquatic plant. Native plant societies usually have specific information about its status in a particular area, for people who are curious.

Ducks feed on duckweed.
Ducks feed on duckweed.

Any plant in the genus Lemna can be considered a duckweed. They usually have small vestigial roots, if they have roots at all, and they grow in the form of thick green carpets of rounded free-floating thalloids, flattened structures which resemble leaves. Duckweed can rapidly spread to cover a waterway, resisting all attempts to eliminate it. These plants typically reproduce by budding, although they can produce small flowers on occasion, and it prefers water which is rich in nitrogen and other nutrients.

In some cases, duckweed can be a boon. The plant readily filters substances, including toxins, out of the water, and some biologists use it in phytoremediation. It can also provide shelter for aquatic animals, in addition to nutrition for larger creatures like ducks and geese. Some species are even considered attractive, making them potentially appealing as ornamentals in the garden. Some scientists have even genetically engineered duckweed to perform specific functions.

This plant can quickly turn into a major problem, especially in areas where water is polluted with excessive nutrients, such as fertilizer runoff from farms, or spills from manure pits at confined animal feeding operations (CAFOs). Well-nourished duckweed can spread rapidly across a body of water, choking out native plant species and threatening resident fish. The plant can also clog propellers and filtration systems, making it a nuisance to humans as well as animals.

If duckweed suddenly appears in an area where it has not been present before, this can be a sign that something about the environment has changed. Droughts, nutrient pollution, and unusual weather patterns can all create blooms, and a proliferation of the plant should be regarded as a cause for concern until the cause has been identified. Some gardeners like to use duckweed as an ornamental for their water features, but they should think carefully before doing this, as it can get out of control or spread to local bodies of water.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


You've definitely got it right about duckweed providing shelter for aquatic animals. Most fishermen find the water plants to be good hiding spots for bass. We love to find this kind of cover because where know there are lunkers lurking beneath them. Any kind of heavy vegetation like this makes good hiding spots.

One thing that is important for fishermen and boaters to do is make sure all of this duckweed is cleaned from the boat when the boat is taken out of the lake. Some fish and game departments are afraid the stuff will spread to another part of the lake, or even to a different lake. In spite of all of its benefits, it sure can be a problem.


My neighbor's pond, which borders my property, became covered with little green leaves one year. Before reading this article, I had no idea what they were.

From a distance, they looked like algae. They grew to cover the entire surface of the pond. When the wind would blow, the water would momentarily peep out as the duckweed moved to the side, but as soon as the breeze subsided, the pond became a solid green sheet again.

I examined the duckweed up close. It looked like the leaves of a three-leaf clover. What surprised me was that the green covering was not just a surface sheet; it had little stems extending down from each leaf cluster!


@MalakAslan – Did your sister find a way to get rid of the duckweed? It is such a widespread problem that you can find a lot of duckweed information on the Internet.

I have been reading about duckweed treatment and I found some companies on the Internet that sell some type of biological bacteria that will clean up duckweed and sludge.


The pond on my sister's ranch has been over run with Duckweed. She was telling me that she read that it reproduces so fast that a single Duckweed plant can become over 17,000 plants in two weeks!

Now that is invasive! She also learned that it can be brought in by migrating birds that land on your pond.

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