Kestanbol geothermal field, located in the ancient town of Alexandria Troas, is at the contact between plutonic intrusions and neighboring metamorphic rocks in the Biga Peninsula. This area is also controlled by an ENE-WSW striking right lateral strike-slip fault segment representing the extension of the southern branch of the North Anatolian Fault to the west and is one of the geothermal fields with highest temperature in the Biga Peninsula. Kestanbol geothermal fluid from a well is used to heat facilities for thermal tourism and balneological purposes. The geothermal fluid continuously seeps into the environment with low flow rate and additionally, wastewater from the facility is discharged into Ilica stream. This study was conducted to determine the hydrochemical characteristics of the well and springs located in Kestanbol geothermal field and to evaluate the environmental effects of geothermal fluids on the soil and stream sediment. The temperature, electrical conductivity (EC) and pH of Kestanbol geothermal fluids are 59.5-74.1 degrees C, 30.3-35.5 mS/cm, and 6.45-6.71, respectively. The geothermal fluids are NaCl water type, with mean NaCl concentration of 19511 mg/L. In addition to higher EC values, and total dissolved solid content, Na+, Cl-, B, Ba, Fe and Mn concentrations of the Kestanbol geothermal fluid are above the tolerance limit of TS 266. Moreover, the geothermal fluid is heavily polluted water (class IV) according to the Turkish Inland Water Quality Regulations in terms of EC, Na+, Cl-, B and Fe. There is a scaling problem in the Kestanbol geothermal field. XRD and SEM-EDX analyses identified the minerals causing scale as calcite, halite and siderite. Arsenic, Fe and Mn concentration of scale, soil and stream sediment samples are higher than the mean value of world continental crust. According to the enrichment factor and geoaccumulation index, the geothermal fluid with intense rock interaction enriches soil and stream sediment in terms of As and Mn metal(loid)s as a result of discharge. It is recommended that geothermal fluids and waste waters from the facility should not be discharged into the soil and Ilica stream.