Photos were lifted from the zoom presentation
With a surface area of 340 square kilometers (its maximum length is 33 kilometers and its maximum width is 22 kilometers), Lake Lanao is the largest lake in Mindanao. It comes second to Laguna Lake (surface area of 911.7 square kilometers) as the country’s largest lake.
Interestingly, Lake Lanao – located in Lanao del Sur – is one of the world’s 17 ancient lakes. Scientists believe the lake is about 10 million years old. As such, scholars have been pushing for the lake’s inclusion in the World Heritage List of the United Nations Educational, Scientific, and Cultural Organization (UNESCO).
“The lake was formed by the tectonic-volcanic damming of a basin between two mountain ranges and the collapse of a large volcano,” Wikipedia states. “It has a maximum depth of 122 meters (400 feet) and a mean depth of 60.3 meters (198 feet). The basin is shallowest towards the north and gets progressively deeper towards the south.”
Four rivers feed the lake. “Its only outlet is the Agus River, which flows northwest into Iligan Bay via two channels, one over the Maria Cristina Falls and the other over the Tinago Falls,” Wikipedia notes. “A hydroelectric plant installed on the Lanao Lake and Agus River system generates 70% of the electricity used by the people of Mindanao.”
Lake Lanao is home to the Meranaw tribe. The name Meranaw was derived from the lake’s name, and it means “the people living around the lake.” It is also the spoken or language of the Maranao people.
Despite the growing population near the lake’s vicinity, the water remains clean, a recent study shows. “Our Lake Lanao, from all sampling sites, is still pristine; our water is still clean,” said Dr. Fema M. Abamo, a professor of Mindanao State University in Marawi City.
She said those words during her webinar presentation for the regional basic research caravan for Bicol. The caravan was initiated by the Department of Science and Technology-National Research Council of the Philippines (DOST-NRCP).
The water quality of Lake Lanao in five samplings was monitored for two years by using the abundance of one-celled protozoan ciliates as bio-indicators of organic pollution. The sampling sites were located in Marawi City, Ramain, Balindong, Taraka, and Binidayan.
The highest ciliate abundance was observed in the littoral zone of Balindong at 0.0061cells/mL during the dry season. A previous study was done in 1989 categorized lakes as ultra-oligotrophic when their ciliate abundance is equal to or lower than 2.4cells/mL.
Ciliates are single-celled organisms that, at some stage in their life cycle, possess cilia, short hair-like organelles used for locomotion and food gathering. Most ciliates are free-living forms.
The findings of the recent study placed Lake Lanao in the ultra-oligotrophic category as its ciliate abundance was below the set range in all sampling sites. “Such lake category has very low nutrients, scarce growth of plants and algae, and high dissolved oxygen indicative of a clean, healthy, good water quality and not organically polluted lake,” reported Geraldine Bulaon-Ducusin of S&T Media Service.
Organic pollution occurs when large quantities of organic compounds are released into aquatic ecosystems. Sources of pollution usually come in the form of wastes generated by farmers and those engaged in agricultural production, residents living in the area, and industries.
When high levels of inorganic nutrients like nitrogen and phosphorus are present in water, the plants and algae may overgrow. When these overgrown plants and algae die, they become organic materials in the water.
“Decomposition of these organic materials uses up high amounts of oxygen, thus depriving the fish population of needed oxygen that causes fish kills in the lake,” Bulaon-Ducusin wrote. “These decaying organic compounds serve as substrates for the microorganisms, increasing the bacterial population which in turn supports the abundant growth of ciliates.”
It must be recalled that in June 2018, 11 towns in Lanao del Sur were affected by fish kill in the lake area. Among the causes cited was “depletion of oxygen due to changes in water temperature.”
Ciliate abundance in the lake varied as the season changed. That is, lower in the non-mixing season and higher in the dry season, indicative of nutrient and organic load fluctuations in the lake as the season changed.
According to Bulaon-Ducusin, water samples for the study were obtained from 50-100 meters away from the lakeshore in the shallower littoral zone and towards the deeper open water in the pelagic zone.
The results of the study were corroborated by the findings of another group in the same program conducting the physical and chemical characterization of the lake. They found that the lake is not polluted but still healthy and has good water quality.
The study, funded by the DOST-NRCP, was conducted during a three-year period but was temporarily suspended when the five-month-long armed conflict in Marawi happened. It was allowed to resume only after the Marawi siege.
“The lake was reportedly deteriorating due to increased human population and activities around the lake,” Dr. Abamo said, explaining why there’s a need to conserve the lake’s good condition, especially now that the people have resettled back near the lake after the Marawi siege.
The researchers suggested to the local government to strengthen their policies to maintain the healthy condition of the lake.
“We have recommended to the local government to create and implement stricter policies and ordinances to conserve the lake and regulate and check both the residential and business establishments around the lake,” Dr. Abamo said.
In 1965, Lake Lanao was renamed by Republic Act No. 4260, then repealed by Republic Act No. 6434 in 1972. In 1992, it was proclaimed as a watershed reservation through Presidential Proclamation 971 to ensure the protection of forest cover and water yield for hydropower, irrigation, and domestic use.
The lake is home to 18 endemic cyprinids (freshwater fishes related to the carps and minnows). Unfortunately, 15 of them are now extinct in the wild, and two more species could also be possibly extinct, the latest International Union for Conservation of Nature (IUCN) Red List of Threatened Species showed.
The extinct species are Barbodes amarus, B. baoulan, B. clemensi, B. disa, B. flavifuscus, B. herrel, B. katolo, B. lanaoensis, B. manalak, B. pachyceilus, B. palaemophagus, B. palata, B. resimus, B. tras, and B. truncatalus.
B. lindog and B. sirang are considered “possibly extinct” or “critically endangered.” A confirmation, like thorough more extensive surveys, is needed, IUCN said, to determine if they are “in all probability already extinct.”
Several reasons were cited why these fish species became extinct. Among those mentioned were overfishing and pollution. Another possible cause: the introduction of 12 different non-native fish species.
The lake also supports a large number of waterfowls. Six bird species can be found in the watersheds surrounding the lake, including white-collared kingfisher, slender bird crow, and cattle egret.
Lake Lanao is also facing other environmental problems. In October 2006, a study done by the Mindanao State University discovered massive algae contamination in the lake. Initially, poor sewage and agricultural waste management were seen as the culprits.
But the Bureau of Fisheries and Aquatic Resources (BFAR), a line agency of the Department of Agriculture, saw otherwise. It stated that soil erosion from indiscriminate logging and extensive land use and farming were the problems that caused the algae contamination.
“For generations, Lanao Lake has been a potent natural resource that breathes life to the Maranaws, as a source of their food and water, livelihood, religious practices, transportation and sports,” Bulaon-Ducusin wrote.
“But more than anything, the lake has shaped the Maranaw culture and tradition to what it is now and it has become imperative for the Maranaws to preserve its pristine beauty for a better and sustainable future,” she concluded.