An aerated wastewater stabilization lagoon, or any subsection of the overall lagoon, should function as an oxidation reactor, a clarifier, and a sludge digester. A relatively simple set of calculations can be used to evaluate these three functions for zones within a lagoon system. Only SBOD, TSS, and NH4-N or PO4-P measurements are needed to support the analysis. The evaluation should be limited to bacterially dominated zones of a lagoon system, i.e. lack of significant algal influence.