| Lake Lanao | |
|---|---|
| Landsat photo | |
| Lake Lanao-Agus River watershed map | |
| Location | Lanao del Sur |
| Lake type | Rift Lake |
| Primary inflows | 4 tributaries |
| Primary outflows | Agus River |
| Basin countries | Philippines |
| Max. length | 33 km |
| Max. width | 20 km |
| Surface area | 340 km² |
| Average depth | 60.3 m |
| Max. depth | 112 m |
| Shore length1 | 115 km |
| Surface elevation | 700 m |
| Settlements | Marawi City |
| 1 Shore length is not a well-defined measure. | |
Lake Lanao (Maranao: Ranao or Ranaw)[1] is a large lake in the Philippines, located in Lanao del Sur province in the country's southern island of Mindanao. With a surface area of 340 km². (131 square miles), it is the largest lake in Mindanao, and the second largest lake in the Philippines and counted as one of the 15 ancient lakes in the world.
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The lake was formed by the tectonic-volcanic damming of a basin between two mountain ranges and the collapse of a large volcano. It has a maximum depth of 112 meters, and a mean depth of 60.3 meters. The basin is shallowest towards the north and gets progressively deeper towards the south.
The lake is fed by four rivers. Its only outlet is the Agus River, which flows southwest into Iligan Bay via two channels, one over the Maria Cristina Falls and the other over the Linamon Falls. A hydroelectric plant installed on the Lanao Lake and Agus River system generates 70% of the electricity used by the people of Mindanao.
The lake is a home of myths and legends of the Maranao tribe. The name Maranao was derived from the name of the lake and it means "the people living around the lake".
Lake Lanao was proclaimed as a watershed reservation in 1992 through Presidential Proclamation 971 to ensure protection of forest cover and water yield for hydropower, irrigation and domestic use. The watershed occupies an area of 153,008 hectares and is home to a rich variety of flora and fauna, including 18 cyprinid species that are endemic to the lake.
As early as the 1980s the scientific community has warned that these endemic cyprinid species may be in danger of extinction due to the long term effects of the hydroelectric plants on lake levels and introduction of invasive alien species. Today, water inflow and outflow have declined, lake water level has decreased, and lakebed exposure has been observed. The accidental introduction of white goby (Glossogobius giurus) in Lake Lanao has also caused the decline of endemic cyprinids (Guerrero, 2002), with only about 5 of 18 species still remaining in the lake
A recent study by the Mindanao State University (MSU) in 2006 discovered massive algal contamination due mainly to soil erosion from indiscriminate logging in the watershed and extensive land use and farming in the surrounding areas (Gallardo, 2006). Other factors that contribute to the deterioration of the lake are the environmental impacts of the dams, hydrological alterations, diminishing waterflow and pollution. If this continues, food security and the livelihood of communities who are dependent on the lake may be seriously affected.
A Lake Lanao Watershed Protection and Development Council (LLWPDC) was created in 1992 responsible for the development of the Lake Lanao Integrated Development Plan (IDP) in 2003. However, the perennial changes in leadership in the Council have made it difficult to implement its mandate. The IDP aimed to manage the Lake Lanao - Agus River Watershed using the landscape approach by harmonizing the various frameworks and activities that have been at work for many years (LLWPDC, 2003). However, current institutional arrangements have not really arrested the degradation of the lake.
Some current initiatives are those provided by the USAID EcoGov2 Project for ridge to reef planning and capacity building of stakeholder groups in the area. The DENR-River Basin Control Office (RBCO) is also supporting the preparation and completion of the Lake Lanao Integrated River Basin Action Plan and the creation of the Agus River Basin Project Management Office. Agroforestry projects, watershed rehabilitation and institutional strengthening are ongoing but harmonization of efforts, sustained management interventions and stakeholder support are keys to saving Lake Lanao.
A Maranao myth describes the formation of the lake[1][3]. It is said that a group of angels under the command of Gabriel removed the vast population of Mantapoli to prevent the world from tipping over. The hole that was left was filled with water and threatened to drown the rest of the world. In response, the angels enlisted the help of the Four Winds to gouge out an outlet. The hole became Lake Lanao and the outlet became the Agus river.
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