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Water Q & A - Duckweed in a Lagoon

Duckweed, Nebraska Extension Acreage Insights September 2017.

Do you have questions about your private drinking water supply?  How about wellhead protection, including the management of your private sewage treatment system?  Send your questions using the Ask An Expert feature on this web site.  Questions will be addressed by Nebraska Extension Educator Meghan Sittler, Nebraska Extension Specialist Bruce Dvorak,  and/or  Nebraska Extension Educator Katie Pekarek. One question and answer will be featured each month in this section of the acreage web site.

Q: Why is my lagoon covered with duckweed and what can I do about it?

Meghan:  Duckweed and other types of algae commonly appear during warm summer months.  Their appearance which can often be relatively sudden are called algal blooms.  Duckweed and other types of algae feed off nutrients such as phosphorous that are in wastewater.  Microbes and other organism are essential parts of the treatment of wastewater within the lagoon as they digest the nutrients and other select contaminants within the wastewater.  You will notice that the water in your wastewater lagoon will often change to a green color as part of the normal “turnover” of your lagoon and the results of that digestion process.  However if a layer or cap of algae such as duckweed appears on your lagoon this can actually impeded the normal function of your lagoon by blocking evaporation, oxygen levels and limiting the activity of the good microorganisms. 

Duckweed can be a nuisance to eliminate from your lagoon as even a few individual weeds left behind can multiply quickly.  Options to remove duckweed range from mechanical to chemical.  You can attempt to rake the duckweed from the surface. If you have a smaller lagoon this may be an option but regardless will be labor intensive and will need to be done multiple times.  Another alternative is to use an aquatic chemical to treat the duckweed.  It is extremely important to follow the mixing and application guidelines of the aquatic chemical.  Duckweed on the surrounding berm will also need to be treated and more than one application of the aquatic chemical may be necessary.  At least some of the treated duckweed once it appears dead should be removed to no add additional organic material into the lagoon.  If you continue to have recurring problems with duckweed even after multiple or seasonal applications you may need to consider hiring a certified professional to check the sludge level in your lagoon.

Meghan Sittler
Meghan Sittler
Extension Educator - Domestic Water & Wastewater
Meghan's education includes a master's degree in natural resources with minors in political science and environmental planning. She also has a graduate certification in public policy analysis, as well as undergraduate degrees in environmental studies and anthropology from UNL. Her graduate project was focused on the development of collaborative and adaptive management for the Missouri River.

Sittler began as coordinator of the Lower Platte River Corridor Alliance in December 2008. Prior to that, Sittler worked for the National Park Service as an archaeological technician, an environmental educator with the Lincoln Lancaster County Health Department, an adviser and instructor with the UNL Environmental Studies program and School of Natural Resources and as a research and outreach specialist for the National Drought Mitigation Center. Meghan began her work as a Nebraska Extension Educator focussing on water in 2016.

Lancaster County Extension Office
444 Cherrycreek Rd
Lincoln NE 68528-1591