Sludge lagoons have been part of the treatment and disposal of wastewater solids since the first introduction of wastewater treatment. They have provided treatment including concentration, stabilization, dewatering (drying), and disinfection at minimum cost and energy use. In many localities, they have also been used for the ultimate disposal of all the treatment plant solids. It is this latter use and the increased quantities of wastewater solids and decreased levels of public tolerance of wastewater treatment nuisances that has brought the use of sludge lagoons into ill repute. An author of a recent book on wastewater solids treatment and disposal goes so far as to say that ultimate disposal lagoons (so-called permanent lagoons) tend to fill up about the time the design engineer retires from active practice leaving his readers, in this author’s opinion, with the firm impression that reputable engineers do not use sludge lagoons in up-to-date wastewater treatment design.