This study evaluates the influence of YanÃ½klar Creek on the water quality of Fethiye Gulf. Accordingly, this study demonstrates (i) change in the water quality of Fethiye Gulf from 2006 to 2007; (ii) the water quality classification of the YanÃ½klar Creek feeding Fethiye Gulf; and (iii) how land-based fish farm influences YanÃ½klar Creek water quality in a Fethiye-GÃ¶cek Specially Protected Area. In this study, the high contribution of nitrite-nitrogen, total phosphate and number of total and fecal coliform of YanÃ½klar Creek is verified to be due to land-based fish farm located on the creek. Since, ammonium nitrogen, nitrate nitrogen, nitrite nitrogen and total phosphate concentrations and, number of total and fecal coliform were elevated and dissolved oxygen levels dropped at downstream of the fish farm. Water transparency increased except in July and August. Number of total coliform increased except in October and November. The number of total coliform in the gulf also dramatically exceeded the acceptable limit of 1000 CFU/100mL, thereby implicating wastewater inputs to the gulf as the probable source. Overall data suggest that external phosphorus and nitrogen loads to Fethiye Gulf derive mainly from tributary streams impacted by point sources, and landbased trout fish farm.