Lake Büyükçekmece (Turkish: Büyükçekmece Gölü) is a liman formed at the point where the river Karasudere flows into the Marmara Sea. The lake is located south of the Çatalca district, west of Istanbul, Turkey. It is used as a freshwater reservoir.
The lakes bar was reinforced in 1988 by a dam. The area of the lake is 28.47 km2, and is 7 km long and 2 km wide. The maximum depth is 8.6 m, following deepening carried out by the State Hydraulic Works.
The fluvial lake developed as the flow of Karasudere, and as it came downwards from Çatalca it was blocked off and formed by the resulting sandbank it created. A reedy, brackish salt-water lake exists between the Büyükçekmece Dam and the Marmara Sea. Another lagoon, Lake Küçükçekmece, is located around 12 km east of Lake Büyükçekmece.
The number of fish species observed in the lake has decreased from 30 in the past to 15 currently.
