Mälaren (historically occasionally referred to as Lake Malar in English) is the third-largest lake in Sweden (after Vänern and Vättern). Its area is 1,140 km² and its greatest depth is 64 m. Mälaren spans 120 kilometers from east to west. The lake drains, from southwest to northeast, into the Baltic Sea through the Södertälje Canal, Hammarbyslussen, Karl Johansslussen and Norrström. The easternmost bay of Mälaren, in central Stockholm, is called Riddarfjärden. The lake is located in Svealand and bounded by the provinces of Uppland, Södermanland, Närke, and Västmanland. The two largest islands in Mälaren are Selaön (91 km²) and Svartsjölandet (79 km²).

Mälaren (historically occasionally referred to as Lake Malar in English) is the third-largest lake in Sweden (after Vänern and Vättern). Its area is 1,140 km² and its greatest depth is 64 m. Mälaren spans 120 kilometers from east to west. The lake drains, from southwest to northeast, into the Baltic Sea through the Södertälje Canal, Hammarbyslussen, Karl Johansslussen and Norrström. The easternmost bay of Mälaren, in central Stockholm, is called Riddarfjärden. The lake is located in Svealand and bounded by the provinces of Uppland, Södermanland, Närke, and Västmanland. The two largest islands in Mälaren are Selaön (91 km²) and Svartsjölandet (79 km²).