LAKE TOBA 

World's Greatest Volcanic Lake in North Sumatra

Bathymetry

Basin Development

Land Use

Nutrient Inputs

Excess Vegetation Growth

The Needs

Monitoring

+Lake Toba, formed some 80,000 years ago in one of the world's largest volcanic explosions, is in North Sumatra, Indonesia. It is the world's largest crater lake and has two major basins and two small ones, remarkable water clarity and great volume of 240 cubic km of deep, blue waters. It is the ninth deepest lake in the world with the depth of 529 m and surface area of 1,130 square km. The drainage basin is only 2,568 square km with 294 streams, composed mainly of basaltic rocks. The sedimentary rocks of Samosir Island, the size of Singapore, are sand and gravel deposits. Lake Toba and its surroundings are the homestead of the exuberant Batak tribe who inhabited these highlands many millennia ago. In Southeast Asia Indonesia possesses abundant supply of clean lake water, of which Lake Toba is more than half.

Mark Twain has described the beauty and remarkable transparency of Lake Tahoe in the United States in his book "roughing It". The same description applies to Lake Toba, which is similar crater lake as Lake Tahoe. If you lower a white plate into water in the middle of Lake Toba it can be seen as deep as 15-18 m. This indicates a really good water quality and state of lake. If the lake was heavily eutrophic or polluted the plate could be seen only down to 0.1 m, a condition possible locally close to some townships.

Lake Toba is ecologically sound. Although there is no long-term data, a good entry point for comparison is available from 1929. The renowned developers of limnology Franz Ruttner, Einar Naumann and Heinrich J. Feuerborn made the first scientific observations at Lake Toba in 1928-29 during the Sunda Expedition and reported their findings in numerous publications. The latest is from 1952. Lehmusluoto and his colleagues report observations of the Expedition Indodanau of 1991-1995 in 1995, 1997, 1999, 2000, 2001, 2002 and 2003 and Acreman and coworkers in 1993, Schmitz 1994, Thomas 1995, Ratulanggi in 1995 and RIWR 2003.

Data of the two expeditions show that major change has not occurred, except some local disturbances close to the townships and tourist facilities. However, there are examples in other parts of the world that also great crater lakes like Lake Toba can quickly change. One is Lake Tahoe.

The recent strive to save Lake Toba has lead to unnecessary disputes, great economic losses, and human suffering and misery. The case needs to be reevaluated. Since 1929 great changes have not occurred in ecology and water quality. However, water level oscillations have become pronounced after the regulating dam of PLTA Asahan at Siruar started its operations in 1982, and the lake suffers now "blue water" shortages. As the local people say there is a hole on the bottom. However, neglecting problems do not solve them. Best practice in water demand is rational appropriation for all water uses, addressing efficiency, equity and ecological soundness.