The aim of this study is to determine the bacteriologi-cal water quality and the incidence of enteric bacteria in the Gulf of Gemlik by means of GIS analysis. Because of the difficulty of individually determining of all types of bacteria in the surface water, the enteric bacteria were cate-gorized in terms of the dominant species and their bacterial composition in the coastal area were also investigated in details. Eleven sampling stations were selected for con-ducting the measurements on a monthly basis during the July 2010-May 2011. The physico-chemical parameters were measured insitu at all sampling stations and the density and the bacterial identification of the species in the enteric bacteria were also determined in the Gulf of Gemlik. During the spring and summer period, the bacterial den-sity was observed to be reduced. However, when the envi-ronmental factors began to change, such as an increase in temperature, different genera were identified. At the litto-ral stations 6, 7 and 8, the density of the enteric bacteria were determined to attain higher values, except for the cold season, because of the negative effects of anthropogenic pollutants carried by various different loads. The results obtained by the GIS analysis pointed out those differences in enteric bacteria species with respect to varying loca-tions. The results reveal that the study area faces bacterio-logical pollution and the existing pollution level in this area is above the criterion level that is specified for aqua-culture, fishery and recreational activity. Employing mod-ern tools like GIS helps us better to understand the spatial distribution of enteric bacteria in the sea. These tools might also be used as the initial steps of determining and provid-ing the input data for water quality modeling studies.