During the program an evaporative waste treatment system for onshore treatment of sewage from watercraft retention systems was developed and demonstrated. Wastes and chemical additives associated with recreational watercraft holding tanks were characterized by analyses of sewage samples obtained from marina and watercraft retention tanks utilizing both freshwater and seawater flushed sanitary systems and by a survey of typical chemical additives employed as bacteriostatic and odor reducing agents. An evaporative waste treatment system was evaluated by testing a propane-fired evaporator for 224 hours with in-house sewer wastes and wastes collected from marina holding tanks. The evaporative system treated 4,590 liters (1,212 gal.) of sewage and concentrated the total solids of the sludge from the initial 0.5% to 12.4% before servicing and removal of the concentrated sludge was required. Although the incineration of the sludge was feasible, the available incinerator was too small to handle all the sludge which could be produced by the continuously operating evaporator. Continuous operation of the evaporator requires approximately 1.0 x 1,000,000 kilocalories per 1000 liters of wastewater evaporated (15 x 1,000,000 Btu/1000 gal.); the actual costs depend on the fuel used and its price.