lake in the Barisan Mountains, north-central Sumatra, Indonesia. It covers an area of about 440 square miles (1,140 square km), excluding Samosir Island, which occupies a large part of the lake's centre and which is about 30 miles (50 km) long and 10 miles (15 km) wide. The lake drains east through the Asahan River into the Strait of Malacca; along the Asahan River several major hydroelectric projects were completed in the 1980s to supply power for industrialization of the lesser-developed areas of northern Sumatra. A high-quality aluminum-processing and smelting centre was also completed in 1984 at the mouth of the Asahan on the coast.