A properly functioning lagoon should be maintained on a regular basis. This includes keeping the berms free of trees and weeds and ensuring that no animals are burrowing in the berms. The water of the lagoon should be a green color, due to the algae present, and be reasonably free of cattails. The lagoon should have little to no odor. Cattail and duckweed are two weeds that tend to multiply rapidly, thrive in the sewage environment, and take over the entire lagoon if allowed.
A few duckweeds will not hurt a lagoon, but if the duckweeds become so dense that they block out the sunlight, they can be detrimental to the healthy balance that the lagoon needs to maintain to function properly. The dense cover will reduce the light, killing the algae, thus reducing the oxygen level in the lagoon. This may cause an odor problem and the duckweed need to be controlled. These weeds may be controlled by chemical or physical means. Chemical works best, but either method may be short lived as one duckweed can reproduce to cover 10 square feet in one day.