Between March and September, we get a lot of calls and questions at the Extension Office about aquatic plant and algae control from owners of private and commercial ponds and lakes.

Aquatic plants and algae form when the water is warm, stagnant and has a lot of excess nutrients, particularly phosphorus.

In most cases, aquatic plants and algae are beneficial to aquatic environments. However, some types of algae can harm humans and other vertebrates. Too much aquatic growth can cause management problems for people and livestock, and even the fish in the water. Large amounts of aquatic plants and filamentous algae can create problems for swimming, fishing and pumping water.

Some of the more common aquatic plants and algae include:

• Cyanobacteria (Blue green algae): This often forms a green or bluish green film, some call it an oily look, visible on the water’s surface and in the water that is called an algal bloom. They may cause the water to smell like rotting plants. While not all forms of cyanobacteria are dangerous, some can be harmful to people, pets and wildlife when the toxins they produce reach high levels.

• Euglena blooms: algae-like mobile organisms that may form a red or orange surface film and add a similar color to the water. It can make the water have an almost rusty look. Some types of euglena blooms can release toxins that cause a fish kill.

• Filamentous algae (pond moss): green, hair-like fibers that may form dense surface mats that float up from the pond bottom. This is the most common type that I get calls on in Boyd County.

• Duckweed: small, floating leaves with tiny, hair-like roots attached to the underside. They are mostly round.

• Watermeal: floating, tiny green, gritty particles that will feel like sesame seeds or cornmeal when rubbed between the fingers. They can look like a very small version of duckweed.

• Creeping water primrose: a reddish vine, with variable shaped leaves that grows in shallow water. It will eventually get a small, yellow flower and can develop thick, shoreline growth and extend into the pond.

• Pondweeds (yes, that is their actual name, not just a generic name of many plants that grow in ponds before they are identified): submersed plants that grow in shallow water and have either long or small oval leaves that grow alternately on the plant’s stem.

If you are concerned about the aquatic plant or algae growth in your pond or lake, contact us and we can help you identify what you have, which is the first step in the managing and controlling them. You can give us a call to come out and look at the pond and weeds, or bring some by the office. The sample needs to be of complete plants, leaves, stems, roots and all. Bring in several in damp paper towels. Older, dried out samples make ID much more difficult.

Close-up, digital images of aquatic plants and algae also can be used for identification. To make sure we can clearly see the plant, take the picture while floating a small amount of the fresh plant material in a shallow, white pan filled with water. It helps if you can separate a few strands of the plant sample in the pan. You can email digital plant images for identification to:   Be sure to include your phone number with the email, as we may have some follow-up questions.

To help us give you the safest and most effective management recommendation, we also need to know your intended use for the water, i.e. water for livestock, fishing, grandkids swimming hole, etc. Some herbicide and algaecides have label restrictions based on specific intended uses.

More information on aquatic plant control and other pond management topics are available at the Boyd County Extension Office or by contacting Kentucky State University’s Division of Aquaculture. Texas A&M University’s website also has a lot of good information about aquatic plants and their control. But if you are doing your own research, make sure the information you are reading is resent and/or the most up-to-date. Also be aware that some herbicides and algaecides may not be legal in all states.

LYNDALL HARNED is Boyd County Extension agent for agriculture and natural resources.

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