In areas of high organics there is frequently evidence of rapid sewage fungus colonization. Sewage fungus appears as slimy or fluffy cottonwool-like growths of microorganisms which may include filamentous bacteria, fungi, and protozoa such as Sphaerotilus natans, Leptomitus lacteus, and Carchesium polypinuym, respectively. The various effects of the sewage fungus masses include silt and detritus entrapment, the smothering of aquatic macrophytes, and a decrease in water flow velocities. An accumulation of sediment allows a shift in the aquatic system structure as colonization by silt-loving organisms occur. In addition, masses of sewage fungus may break off and float away, causing localized areas of dissolved oxygen demand elsewhere in the water body.
Organic levels decrease with distance away from the source.
In a standing water body such as a lake, currents are generally not powerful enough to transport large amounts of organics. Hence, there is a decline in the oxygen demand and an increase of dissolved oxygen in the water. Community structure will gradually return to ambient with distance downstream from the source. Domestic pet excreta may also contribute. Sewered communities may not have enough capacity to treat the extremely large volume of water resulting from large rainfalls.