Sapanca Lake (Sapanca Gölü in Turkish) is situated in Sakarya province. It's a very well-known and popular tectonic freshwater lake in northwestern Turkey, conveniently located relatively close to Istanbul, making it a very popular weekend getaway and day trip destination for residents of Istanbul and surrounding cities like Izmit (Kocaeli) and Adapazari (Sakarya). It's a major center for recreation and tourism. People visit for its natural beauty, recreational opportunities, relaxing atmosphere, and various activities such as canoeing, pedal boating (SUP - stand-up paddleboarding), picnicking, walking and cycling. Many cafes, restaurants, and tea gardens line parts of the shore, offering picturesque views. The area has also several spa hotels and wellness centers. The nearby Kartepe mountain offers skiing and snowboarding in the winter, making Sapanca a year-round destination.
The lake is roughly 45 square kilometers (about 17 sq miles) in area. It's fed primarily by streams descending from the surrounding mountains. Its excess water flows out via the Cark stream, which eventually connects to the Sakarya River, which in turn flows into the Black Sea. The lake is a crucial source of drinking water and industrial water for the surrounding region. Due to its popularity, the area around the lake has seen significant development in constructions. This puts pressure on the natural environment. It can get very crowded, especially during weekends and public holidays, particularly in the summer months.