Kalimantan has the largest rivers, including the Mahakam in East Kalimantan and the Martapura and Barito in South Kalimantan.
Most of these rivers originate in the island’s central massif (mountain mass) and meander through extensive swamps as they approach the coast. Settlements such as Samarinda and Banjarmasin cluster along the rivers, which serve as communication routes into the interior.
The largest rivers on Sumatra drain from west to east into the Strait of Malacca.
In the north, the Asahan River once linked trade between the Batak people who live inland and the Malay people who live along the coast.
The Asahan is now dammed, however, and produces hydroelectricity for the industries of North Sumatra.
In the south, river ports such as Jambi on the Hari River and Palembang on the Musi River are located upstream, away from the extensive mangrove swamps and marshes of the coast. Passenger ferries and small riverboats provide services along the main rivers.
Papua has more than 30 major rivers draining to the north and south from the Maoke Mountains, which run through the center of the province.
One of the most significant is the 400-km (250-mi) Baliem River, which rises in the Jayawijaya Mountains and drains into the Arafura Sea. Many tribal groups, including the Dani and the Asmat, live along the river and its tributaries.
This lake is about 1,700 m2 in size with the depth of approximately 450 meters. About 906 m above sea level, this lake hosts various interesting plants.
Some people, viewing the sunrise and sunset around this area, claim that Toba manages to help them forget their problems even though only for a while.
Samosir Island is located proudly in the middle of the lake. Another lake inside Samosir Island makes this place more unique and interesting.
The main rivers of Java include the Tarum and Manuk in the west, the Serang and Serayu in central Java, and the Solo and Brantas in the east.
All meander across the broad lowlands of Java, and several are laden with silt due to the extensive farming in their basins.
Lake Toba, the largest of Indonesia’s lakes, is situated on Sumatra’s Batak Highlands in the Barisan Mountains, about 180 km (about 110 mi) south of Medan.
Surrounded by steep mountain cliffs and sandy beaches, Lake Toba covers 1,145 sq km (442 sq mi) and features Samosir Island in its center. The lake is the source of the Asahan River, and as the center of Batak culture it is an important tourist destination.
Lake Tempe, in the center of South Sulawesi province, is another important lake, although it is shrinking in both size and significance. Tempe is thought to be a remnant of an inland sea that once divided the peninsula on which it sits.
The lake is now fed by the Walanae River and is an important source of fish and shrimp (called lawa), which are used both locally and for export.
In order to make Tempe more productive, the government at one time restocked it with fish that do not compete with each other for food. Because of siltation from nearby farms, Tempe is now less than 2 m (6 ft) deep, and large parts dry up in the dry season.
Other significant lakes include Maninjau, Kerinci, and Singkarak in Sumatra; Towuti, Sidenreng, Poso, Tondano, and Matan in Sulawesi; Paniai and Sentani in Papua; Jempang, Melintang, and Semayang on Kalimantan’s Markaham River; and Luar, Sentarum, and Siawan on the upper reaches of Kalimantan’s Kapuas River.