Seaweed does an important job in the sea by providing food and shelter for sea animals, but it can be a pest in ponds and lakes, killing fish and other plant life and damaging boats. "Seaweed" may bring to mind only the plants you find in the ocean, but it is actually a generic term that can refer to aquatic weeds in lakes and rivers, too. If you get rid of seaweed before it gets out of control, you can lessen the damage. Choose the removal method best suited to the location.
Pond Weed Removal
If seaweed is a problem in your pond, you have a few removal options. You can remove the seaweed manually by wading into the pond and grabbing the seaweed with your hands. A seaweed rake (also called a seaweeder rake) helps to get rid of seaweed near the water's surface.
Grass carp in your pond will eat seaweed and other types of algae. Check with your state's Department of Natural Resources to check for restrictions and find out if you need a permit. For example, in Florida only triploid grass carp are allowed, and a permit is always required.
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Blue or black pond dye hinders the penetration of sunlight into pond water, meaning less seaweed grows. The dye is safe for fish and plants, but make sure you follow the directions on the label to ensure you use the right amount for the size of your pond.
Copper sulfate, available from garden centers and home improvement stores, is an herbicide designed for seaweed. Again, follow all directions and take heed of all warnings on the label.
Lake Weed Removal
Wondering how to get rid of seaweed in a lake? The least harmful method of lake weed control is to use a seaweeder rake. Stand in the safest place and lower the rake into the water, allowing its weighted head to sink. When the head of the rake is at the bottom of the water, slide it along the bottom to let it grip the seaweed, and then pull it out of the water. Repeat until you've removed all seaweed.
An herbicide may also work as a lake weed killer, but make sure it is suitable and safe for use in a large water body first. Contact your Department of Natural Resources to check for restrictions on aquatic plant management activities in public water bodies.
How to Reuse Seaweed
The most environmentally friendly way to reuse seaweed is to turn it into fertilizer or compost. If possible, use fresh seaweed to fertilize your soil before it dries. If adding seaweed to your compost heap, add woody material like paper to reduce the slimy consistency.