How to Control Duckweed With Grass Carp


Duckweed is the name given to a group of small, floating aquatic plants that can multiply and eventually choke out a lake or a pond. There is a balancing act necessary for aquatic plant life--too much and a pond or lake can become "choked," and too little results in no hiding places for fish and a lack of renewed oxygen in the water. One way to thin an overabundance of duckweed is to stock a pond or a lake with hungry grass carp. In order to see a relatively quick reduction in duckweed, the grass carp must be at least 8 to 11 inches long when stocked.

Step 1

Determine how many triploid (sterile) grass carp are needed to clear a lake or pond of duckweed based on the size of the lake. Seven to 15 grass carp per surface acre of pond or lake is generally considered an optimal number. If grass carp of 10 lbs. or larger are being introduced to a lake, then stock at the lower number.

Step 2

Purchase the required number of certified sterile grass carp and release them into the lake or pond.

Step 3

Be patient. Based on the size of the grass carp at the time they were introduced into the lake or the pond, it could take an entire year before there is a noticeable reduction in the amount of duckweed on the surface of the pond. Larger fish will consume more duckweed than smaller fish and control the duckweed problem sooner.

Things You'll Need

  • Triploid grass carp


  • U.S. Forestry Service: Got Duckweed? Get Carp!
  • Natural Environmental Systems: Duckweed
  • Penn State University: Duckweed and Watermeal
Keywords: control duckweed, grass carp duckweed, kill duckweed

About this Author

Larry Parr has been a full-time professional freelance writer for more than 30 years. For 25 years he wrote cartoons for TV, everything from SMURFS to SPIDER-MAN.