Lake Lanao
Ancient lake in Mindanao, Philippines, with endemic fish and hydroelectric dams.
Lake Lanao, known locally as Ranao or Ranaw, is an ancient lake in Lanao del Sur, Philippines. Spanning approximately 357 square kilometers, it ranks as Mindanao’s largest lake, the Philippines’ deepest and second largest, and one of just 15 ancient lakes worldwide. The Maranao people, whose name means “those who live around the lake,” are native to its shores.
The lake sits at 700 meters elevation, giving it strong hydroelectric potential. In 1953, the National Power Corporation (NAPOCOR) completed the first plant (Agus VI) along the Agus River system, with Agus I commissioned in 1990. These plants now supply 70% of Mindanao’s electricity. In 1978, the Marawi Lake Regulation Dam was built at the Agus River’s outlet, and five plants (Agus I, II, IV, V, and VII) were soon commissioned. Unlike the others, Agus I sits directly on the lake’s shoreline in Marawi City. This construction effectively turned the lake into a reservoir, sparking strong opposition from the Maranao. In October 1990, as Agus I neared completion, public protests led to the formation of the Save Lake Lanao Movement (SALAM), which aimed to block NAPOCOR’s work. SALAM argued the dam would create an unnatural alternative outlet, causing a 9-meter fluctuation in the lake’s level. The conflict prompted Senator Aquilino Pimentel Jr. to form a task force, delaying the plant’s commissioning until January 14, 1992. Two months after Agus I began operating, President Corazon Aquino declared the Lake Lanao watershed a reservation and created the Lake Lanao Watershed Protection and Development Council, including representatives from both SALAM and NAPOCOR. Despite this, NAPOCOR has made no major concessions, and SALAM and the Maranao continue to protect the watershed.
In 1965, the lake was renamed Lake Sultan Alonto under Republic Act No. 4260, but this was repealed by Republic Act No. 6434 in 1972. Section 22 of Article XIII of the Bangsamoro Organic Law does not place the lake under the Bangsamoro Autonomous Region in Muslim Mindanao, though some Maranao groups had sought its inclusion. In October 2006, a Mindanao State University study found massive algae contamination in the lake.
Quick Facts
- Lake Type
- Ancient lake, Rift lake
- Inflow
- 4 tributaries
- Outflow
- Agus River
- Catchment
- 1678 km2
- Location
- Lanao del Sur
- Countries
- Philippines
- Length
- 33 km
- Area
- 334 km2
- Depth
- 60.3 m
- Max Depth
- 112 m
- Volume
- 21.28 km3
- Shore
- 115 km
Facts from the source article.
Lore & Background
Lake Lanao was formed by the tectonic-volcanic damming of a basin between two mountain ranges and the collapse of a large volcano. It is fed by four rivers—Ramain, Taraka, Gata, and Masiu—and its only outlet is the Agus River, which flows northwest into Iligan Bay via two channels, one over Maria Cristina Falls and the other over Tinago Falls. Four islands lie within the lake: Balutmaito, Balutmasla, Nusa, and Salungan.
The lake was home to 18 endemic species of cyprinid fish in the genus Barbodes, believed to have evolved from the widespread common barb B. binotatus over 10,000 to 20,000 years. However, by 2020, 15 of these endemics were regarded as extinct, with two others possibly extinct, due to overfishing, pollution, and competition from introduced species.
Reader's Guide
Lake Lanao holds significant ecological, cultural, and economic importance. Ecologically, it is one of the world's 15 ancient lakes and once hosted a remarkable radiation of 17 endemic cyprinid fish species, most of which are now extinct or possibly extinct due to human activities. The lake's biodiversity decline highlights the fragility of isolated freshwater ecosystems. Culturally, the lake is central to the Maranao people, who derive their identity from it and preserve myths about its formation. The lake's inclusion in the Bangsamoro Organic Law was sought but not granted. Economically, the lake's hydroelectric plants supply 70% of Mindanao's electricity, but the construction of Agus I turned the lake into a reservoir, causing environmental and social conflict. The Save Lake Lanao Movement continues to advocate for the watershed's protection. The lake's potential UNESCO World Heritage listing remains a goal for scholars.
Did You Know?
- Lake Lanao is one of the 15 ancient lakes in the world.
- The lake was renamed Lake Sultan Alonto in 1965, but the name was repealed in 1972.
- 15 of the lake's 17 endemic fish species were regarded as extinct by 2020.
- The Agus I hydroelectric plant, built directly on the lake's shoreline, turned the lake into a reservoir.
Frequently Asked Questions
What is Lake Lanao?
Lake Lanao, also called Ranao or Ranaw, is a tectonic-volcanic ancient lake in Lanao del Sur, Mindanao, Philippines. It covers roughly 357 square kilometers and plunges to a maximum depth of 122 meters, making it the deepest lake in the country.
Why is Lake Lanao classified as an ancient lake?
It was formed over a very long geological timespan through tectonic and volcanic damming, placing it among only about 15 ancient lakes on Earth. That great age has allowed unique endemic fish species to evolve in isolation within its waters.
Where is Lake Lanao located and how big is it?
It sits at an elevation of 700 meters in the province of Lanao del Sur on the island of Mindanao, Philippines. At 357 square kilometers of surface area and a mean depth of about 60 meters, it is Mindanao's largest lake and the Philippines' second-largest.
What role does Lake Lanao play in electricity generation?
Its high elevation gives the Agus River outflow strong hydroelectric potential, so NAPOCOR completed the Agus VI plant in 1953 and later commissioned Agus I in 1990. These dams harness the lake's water to produce power for the region.
Why is Lake Lanao culturally significant?
The Maranao people, whose name literally means 'those who live around the lake,' have inhabited its shores for generations and built their entire identity around the water. The lake sits at the heart of their traditions, daily life, and sense of place.
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