Diffuse pollution generated from the coastal tourism areas is one of the significant threats for the marine environment. Besides the accommodation facilities discharging the generated wastewater into the sea without any treatment, the summer resorts of the coastal areas also deteriorate the coastal waters. Since most of the summer resorts do not have any sewage system, it is difficult to control these non-point sources. The research was conducted in two phases at selected two beaches and a coastal village having summer resorts in Cesme, Turkey. In the first phase, seawater quality was monitored while the wastewater was discharged/seeped into the marine environment without any treatment. In the second phase, besides the construction of the treatment plants for the wastewater of the facilities, willow trees were planted in the soil near the septic tanks of the summer resorts. During the study, the sea quality was monitored by samples collected during the peak seasons as well as during the low seasons to determine the effect of the population increase on the seawater quality. Growth rates of the foliage and trees were also followed up. During both phases of the research, a questionnaire was distributed to the tourists and the local people to determine the types and the number of incidences of the waterborne diseases they faced. The waterborne disease incidence is actually increasing worldwide, promoted by both natural phenomena and human activities including sewage disposal. This study verified that even small increases in the degree of microbial pollution in seawater results to a considerable increase in the number of waterborne disease incidences. This is a very important observation especially for developing countries which depend economically mainly on tourism. In this study, the results indicated that by the operation of the treatment plants and the application of the willows, the seawater quality was improved and the seaborne disease incidences caused by the sewage disposal were reduced significantly.