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How to Control Duckweed With Grass Carp

By Larry Parr ; Updated September 21, 2017
Triploid grass carp cannot reproduce and eat their own body weight in duckweed every day.

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.

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.

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

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 Will Need

  • Triploid grass carp


  • Given time, grass carp can reduce too much of the plant population, denuding a pond or a lake entirely. To keep this from happening it may be necessary to remove some or all of the grass carp from the lake or pond once they have done their job. Catching grass carp is not easy--bow hunting has proven to be one of the most effective ways of removing grass carp.

About the Author


Larry Parr has been a full-time professional freelance writer for more than 30 years. For 25 years he wrote cartoons for television, everything from "Smurfs" to "Spider-Man." Today Parr train dogs and write articles on a variety of topics for websites worldwide.