Duckweed covers a Waconia pond.

Is your pond or lake covered in green? Naturally, most people assume green on a lake or pond is algae, but often the green on top of your water is duckweed.

Also known as duck’s meat or water lentil, duckweed is actually tiny, free floating native plants. The plants are found in clusters of leaves, each with small roots that hang down into the water. It can form thick green blankets on the water’s surface, which is why it is often mistaken for algae.

Duckweed is found in quiet waters of ponds, lakes and streams and will rarely become abundant on waters with frequent wind or lots of wave action.

Looking at the water from a distance, it’s hard to tell if its duckweed or algae. Get closer and you will either see tiny individual smooth green dots with little roots forming a mat (duckweed), or a mat of fuzzy algae with no indistinguishable pieces.

Duckweed is an important part of the food web in lakes and ponds, providing food for waterfowl and other birds. It also provides shelter and food for small aquatic bugs which can be seen darting here or there between the root systems. These bugs are then food for fish.

By creating a mat on top of the water it keeps algae and mosquito breeding under control, provides shade to keep the water below cool, and even cleans the water. In fact, duckweed is used at many water treatment plants to help purify the water.

As duckweed provides benefits both to water quality and the wildlife many residents enjoy, it should mostly be left alone. On occasion, duckweed can get too thick, and shade out larger, submerged plants. Yet, it reproduces so rapidly that effective control can be difficult.

So relax and enjoy the green-topped water, it means your lake or pond has life and a self-cleaning capability.

Madeline Seveland is an education coordinator with Carver County Water Management. She can be reachedat

Community Editor

Mark Olson, the Chaska and Chanhassen community editor who has worked in Carver County for 20 years, makes any excuse to write about local history. In his spare time, Mark enjoys perusing old books, watching blockbusters and taking Midwest road trips.


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