In this study seawater samples were taken from Ayamama stream’s discharge point and from around of its six different areas every 15 days, and were examined in terms of bacteria such as faecal coliform, total coliform, faecal streptococci, Salmonella spp. and total mezophilic aerobic heterotrophic bacteria from May 2007 to April 2008. It is found that in all of the seven areas from which samples were taken, bacteria counts found are over seawater quality standards. It is found that the area in the best condition is station 6 which is far away 1 km from discharge point and the worst one is station 1 which is discharge point of the Ayamama stream to Marmara sea. Also, it is determined that the number of indicator bacteria show difference depending on months and seasons. Furthermore, a hierarchical ascendant cluster analysis was used to classify the sampling stations into similar groups. Dendograms obtained from cluster analysis has revealed that stations which are far away 500 m discharge point, in front of Air Force Academy (Yeşilköy), an four-star hotel and Yesilyurt sports club were similar at the first level in terms of the number of faecal coliform, total coliform, faecal streptococci and Salmonella spp. However, station 6 which is far away 1 km from discharge point was similar at the second level. As a result, when all findings were examined it was seen that Ayamama stream was a very serious threat for the sea of Marmara.