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Randolph County Health Department
1319 E Hwy 24, Suite A, Moberly, MO 65270


Lagoon Maintenance

What is a lagoon?

On-site Wastewater Lagoons are a natural and effective way to break down and treat wastewater form residences. Lagoons are designed and sized based upon the number of bedrooms in the home. Waste and wastewater flow from the home into the properly constructed lagoon where heavy material sinks to the bottom of the lagoon and is digested by naturally occurring bacteria. A septic tank before the lagoon can improve the quality of the discharge from a lagoon, but is not mandatory unless the lagoon is constructed in a subdivision, on a property of 10 or less acres; or the residence has a garbage disposal. Wastewater in the lagoon is also treated by bacteria, algae, sunlight, and wind. The discharge pipe is allowed in a lagoon, but lagoons generally do not discharge if properly sized except when there are periods of heavy rain.  Click here to see recommended Lagoon Specs.

Lagoon Maintenance:

Lagoon maintenance is easy, if the following precautions are taken:

  1. Keep the berms (outside and inside) mowed. Do not allow trees and tall vegetation to grow in the lagoon as this will cause the lagoon to “go septic” and odors will develop.
  2. The lagoon is not a trash dump.  Do not allow garbage, tires or debris to get into the lagoon.
  3. Do not allow paints, paint thinner or large quantities of chemicals to flow to the lagoon.  Use of chlorine bleach in laundry and small amounts of household cleaners is ok.
  4. Lagoons may develop odors when they “turn over” in the spring and fall.  If this happens and lasts for more than a day or two, add fertilizer to the lagoon.  This will jump start the algae and reduce odors.  Fertilizers containing ammonium nitrate are best.
  5. If cattails get into the lagoon, there are chemicals that will kill them, but they must be pulled out by the roots. The best way to avoid cattails is to keep plenty of water in the lagoon. Duckweed is another plant that can interfere with lagoon operation. It is killed by the same chemical herbicides as cattails.

Septic Tanks ahead of Lagoons:

  1. Septic tanks precede lagoons to extend the life of the lagoon by keeping solids out of the lagoon which eventually build up in the bottom of the lagoon and must be removed.
  2. Septic tanks will need to be cleaned out every 3-5 years by a licensed septic tank pumper.  At that time you should check to assure that your tank is still in good condition and that the baffles are still in place.  Do not however enter into the tank-methane and other toxic gasses can be present.

Fencing Requirements:

  1. The fence shall be at least four feet (4’) in height.
  2. The fence shall be welded, woven or chain link material with no smaller than fourteen gauge wire. Cattle or hog panels can be used with a tee post instead of a line post.
  3. Fence posts must be pressure treated wood, galvanized or painted steel. Fence posts shall be driven, tamped or set in concrete. Line posts should be at least 18” deep and shall be spaced no more than 10’ apart. Corner posts should be at least 24″ deep and shall be properly braced.
  4. If desired, decorative fencing such as white heavy molded plastic, is acceptable so long as it is gated, and sturdy enough to keep animals and children out.
  5. The fence shall be no closer than the center of the berm to the water’s edge at the 3’ operating level, however it is recommended that the fence be placed around the outside perimeter for ease of mowing. Fence set- backs shall be no more than 30’ from the waters edge.
  6. The fence shall be of sound construction with no gaps or openings along the bottom.
  7. A properly hinged 4’ high gate or comparable materials shall be installed and provided with an effective latching device. The gate should be 36-48” in width to accommodate maintenance and mowing equipment.
  8. It is required that the fence be completed prior to occupancy of the residence.

Screen your Lagoon with a Thuja Green Giant

The Thuja Green Giant is the fastest growing evergreen tree.  It grows 3-5 feet per year, once it is established.They are widely grown as ornamental trees, and extensively used for hedges. A number of cultivars are grown and used in landscapes. Usually, homeowners will plant them as privacy trees between them and their neighbors. The cultivar ‘Green Giant’ is popular as a very vigorous hedging plant.

These evergreens grow in a uniform shape and height, without having to prune .  In fact, you don’t have to do anything to them.  They are drought tolerant and have no significant insect or disease problems.  They are tough enough to resist ice and snow damage and grow well in almost any soil, even clay.  They prefer direct sunlight, but also do well in partial shade.

These make an ideal shrub to screen off your lagoon from your home or your road.  As long as they are not planted too close to the berm,  their 20-30 foot height make a thick, compact privacy screen.


Common duckweed (Lemna minor) is a very small light green free-floating, seed bearing plant. Duckweed has 1 to 3 leaves, or fronds, of 1/16 to 1/8 inch in length. A single root (or root-hair) protrudes from each frond. Giant (Spirodela polyrhiza) or big duckweed is still relatively small (1/16 to 1/4 inch) with 1 to 4 leaves, or fronds, light green in color. Three or more roots (or root-hairs) protrude from each frond. Duckweeds tend to grow in dense colonies in quiet water, undisturbed by wave action. Often more than one species of duckweed will be associated together in these colonies and can be an aggressive invader of ponds and are often found mixed in with other duckweeds, mosquito fern, and/or watermeal. If colonies cover the surface of the water, then oxygen depletions and fish kills can occur. These plants should be controlled before they cover the entire surface of the pond.

Dense duckweed colonies provide habitat for micro invertebrates but if duckweed completelycovers the surface of a pond for an extended period it will cause oxygen depletions. These colonies will also eliminate submerged plants by blocking sunlight penetration. Many kinds of ducks consume duckweed and often transport it to other bodies of water.

Duckweed Control Options


Duckweeds can be removed by raking or seining it from the pond’s surface.


Grass carp will seldom control aquatic vegetation the first year they are stocked. Young grass carp will consume duckweeds but are usually not effective control as large fish (over 10 pounds). Grass carp stocking rates to control duckweeds are usually in the range of 7 to 15 per surface acre or higher. In Texas, only triploid grass carp are legal and a permit from the Texas Parks and Wildlife Department is required before they can be purchased from a certified dealer.

Tilapia will consume watermeal but are a warm water species that cannot survive in temperatures below 55° F. Therefore, tilapia usually cannot be stocked before mid-April or May and will die in November or December. Recommended stocking rates are 15 to 20 pounds of mixed sex adult Mozambique tilapia (Oreochromis mossambicus) per surface area. Tilapias are often not effective for vegetation control if the pond has a robust bass population due to intense predation. In Texas, stocking of Mozambique tilapia does not require a permit from the Texas Parks and Wildlife Department. Any other species of tilapia would require a permit. Check with out County Extension Agent in other states for legality of stocking tilapia.
Ducks will eat duckweeds but seldom control them.


The active ingredients that have been successful in treating duckweeds include
diquat (G) and fluridone (E). E = excellent, G = good

Information and photos courtesy of:
Department of Wildlife and Fisheries Sciences, Texas A&M University

For questions on lagoons, call the Randolph County Health Department at 660-263-6643 Ext. 234.

© Randolph County Health Department