What is a lagoon?
- A lagoon is a small pond that receives wastewater from a home for treatment.
The lagoon is three to five feet in depth and the size is determined by the
number of bedrooms in a home. A lagoon works to treat domestic sewage by a biological
How does a lagoon work?
- The sewage from the home enters the lagoon on the bottom. The solids
stay on the bottom and become sludge. Algae, a microscopic plant that lives
in the lagoon, works with carbon dioxide and sunlight to produce oxygen. Other
microorganisms use this oxygen to digest the sewage. This is why sunlight and
good wind action are essential for a lagoon to work properly. Trees must be
cleared around a lagoon for this reason. The lagoon should also be mowed frequently
to make sure the lagoon gets plenty of sun and wind.
What should be done to maintain a lagoon?
- A properly built and maintained lagoon should have little to no odor. The lagoon
may "turn over" in the spring and in the fall and have some odor for
a few days. If the lagoon has an odor at other times there may be another problem.
If a lot of leaves fall into the lagoon, they can cause the lagoon to smell.
When the leaves begin to decompose they produce tannic acid which lowers the
pH of the lagoon. This kills the algae and upsets the biological process that
is treating the sewage. If this occurs, trim or cut the trees that are causing
the leaves to fall into the lagoon. The water in the lagoon can be treated with
2 pounds of ammonium or sodium nitrate per day until the odor dissipates. Odors
can also be caused when something is put down the sewer that upsets the natural
process in the lagoon such as a large amount of chemicals or lack of sunlight
as in extended cloudy weather.
- If the home has a garbage disposal, it is best to have a properly sized and
constructed septic tank preceding the lagoon. The tank should have at least
1000 gallons of capacity. This will reduce the fats and solids that will overload
- The lagoon should be filled with water prior to operation. No additives will
be necessary to start the biological process. The bacteria from the sewage will
be sufficient for this.
- The lagoon banks and area around the lagoon will need to be kept mowed and
free of trees. The banks should be mowed to the water’s edge. This will
prevent tall grass from drooping into the lagoon where it provides mosquito
breeding areas and could contribute to premature filling. Mowing debris should
not enter the lagoon.
- Remove trees within 50 feet of the lagoon to keep leaf debris from entering,
avoid shading the surface and help control tree roots. Remove any other vegetation
or trees which shade the lagoon, especially during the winter months. Watch
for damage to the banks, especially from burrowing animals. Repair any damage
immediately and reseed with grass as needed. Remove cattails and other vegetation
including duckweed and floating algae masses from the lagoon immediately to
minimize mosquito breeding and excess organic loading and to improve oxygen
transfer. To help reduce damage to the banks, keep the fence in good repair
so animals cannot get on the banks.
Return to the Environmental Health Division Homepage or return to the Columbia/Boone County Health Department Homepage