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How to Kill Seaweed in a Pond

Amanda Flanigan

Despite its name, seaweed can grow in abundance in ponds and lakes and easily become an invasive problem. Seaweed chokes out fish and other plant life in a matter of months. Deal with seaweed early, before it gets out of control, with a variety of ways. Use these methods in conjunction with one other for the best possible seaweed control.

Attack seaweed early before it takes over your pond.
  1. Manually remove the seaweed. Equip yourself with a pair of waders and carefully enter the pond. Grab the seaweed and jerk it out of the pond. Toss the seaweed on the bank near the pond. Alternatively, use a seaweed rake to skim the surface of the pond and remove seaweed.

  2. Purchase grass carp and place them in your pond. Grass carp eat aquatic plants and algae such as seaweed. These fish are a natural way to remove seaweed without the use of harsh chemicals. Some grass carp require a permit, according to the University of Florida Extension. Contact your local Department of Natural Resources for more information.

  3. Install a pond aerator, which keeps the water moving consistently and lowers the amount of seaweed in your pond.

  4. Add blue or black pond dye to your pond. Pond dye is not harmful to fish, plants or other aquatic creatures. The dye causes less sunlight to penetrate the water, and less sunlight means less seaweed. Add dye in amounts appropriate for the size of your pond, according to proportions listed on the packaging.

  5. Apply an herbicide such as copper sulfate, which is designed for seaweed. Read all directions and warnings printed on the label. Herbicides are available at local home improvement stores and garden centers.