The River Buyukmelen is located in the province of Duzce in northwest Turkey and its water basin is approximately 470 km(2). The Aksu, Kucukmelen and Ugursuyu streams flow into the River Buyukmelen. It flows into the Black Sea with an output of 44 m(3) s(-1). The geological succession in the basin comprises limestone and dolomitic limestone of the Yilanh formation, sandstone, clayey limestone and marls of the Akveren formation, elastics and volcano-elastics of the Caycuma formation, and cover units comprised of river alluvium, lacutrine sediments and beach sands. The River Buyukmelen is expected to be a water source that can supply the drinking water needs of Istanbul until 2040; therefore, it is imperative that its water quality be preserved.