Domestic sewage effluent into a high mountain valley stream can produce a complexity of effects on receiving waters. Mountain streams are cold waters which have envolved a diverse biological system adapted to cold temperature, clear water and in which sewage effluents can persist for relatively long periods of time. The lower Logan River below the City of Logan is such a stream. It receives comestic effluent from the City of Logan, which at the start of the study went directly, untreated, into the Logan River, and during the course of the study was diverted through an extensive primary-secondary-tertiary treatment lagoon system retuning treated water back to the receiving stream. The physical, chemical and biological qualities of the Logan River were studied before and after treatment. The development of a biological system and its effect on the physical and chemical qualities in the lagoon system, built essentially upon a primordial substrate, were also studied. An annotated bibliography of 250 references on wastewater stabilization ponds i included. Tertiary treatment ponds can be ecologically managed to minimize organic build-up. Design criteria should also be established to maximize retention time to fully utilize the ecosystem developed in the pond. Free-form designs are suggested as a possible means to accomplish this with the added benefit of improving aesthetics of the problem. (WRSIC abstract)