Rising water of Lake Mainit in Caraga: boon or bane?

During the rainy season from November to March, the water level of Lake Mainit rises by at least one meter. When typhoons hit, the lake, which is shared by Agusan del Norte and Surigao del Norte in the Caraga Region, goes up as high as three meters, a team from the Mindanao State University reported.

Locals have called this yearly phenomenon guob. As much of the 62-km shoreline of Lake Mainit consists of rice fields, guob is particularly apparent when thousands of rice fields near the lake are flooded.

Alejandro Felecio, president of Lapucon Farmers Organization said that through the years, many farmers at Lake Mainit have come to understand the pattern.

“Neophyte farmers at Lake Mainit who do not understand the ‘guob’ will only encounter crop failure,” he said. Mr. Felecio added it is actually beneficial to the farmers since rotten rice stalks and leaves become natural fertilizers.

Kaiser B. Recabo, Jr., director of the Lake Mainit Development Alliance (LMDA), said there are two sides to the guob.

On one hand, the rising water is beneficial to the many fish species in the lake as it gives them more space. On the other hand, people who live by the lakeshore complain it destroys their properties.

Siltation, the LMDA director said, is the main cause of guob. Heavy rainfall can easily increase the lake level since water cannot get out considering Lake Mainit has only one outlet -- the 29 km Kalinawan River.

Through the years, Mr. Recabo said, there have been many suggestions to eradicate the guob. These suggestions, he said, include the dredging of the Kalinawan River, construction of a dike system and establishing of other siltation control infrastructures.

Another recommendation was to open up a portion of the mountain that separates Lake Mainit and the Mindanao Sea. Through this opening, the lake water can drain out and be utilized to generate hydroelectric power for the Caraga Region, the LMDA director said.

However, he said the above-mentioned suggestions and recommendations should be thoroughly studied first.

An 18-month feasibility study is under way to study the many options for Lake Mainit, Mr. Recabo said, noting the establishment of a hydroelectric power plant at Lake Mainit has long been on the drawing board of the government.

Based on the report of the Philippine Information Agency in 1994, then president of the National Power Corp. Guido A. Delgado authorized the Agusan Power Corp. to develop the Lake Mainit hydroelectric power plant in the town of Jabonga in Agusan del Norte.

In the Infrastructure Philippines 2010 Summit last month, Energy Secretary Jose Rene D. Almendras said one of the possible projects in Mindanao where the government and private sector could partner is a 25-megawatt Lake Mainit hydropower prospect in Jabonga. The Department of Energy estimated that the project will cost $62.50 million.

But in the ‘Limnological and Water Quality Assessment of Lake Mainit,’ Mindanao State University (MSU) researchers said “the plan to develop a hydroelectric generating plant that would tap Lake Mainit for its water source would certainly have a far-reaching impact on the biology and ecology of some important aquatic plant and animal species thriving in the lake.”

The MSU researchers added that anything that “would allow an excessive fluctuation of the water level in the lake would also have drastic impacts on the ecology of some lakeshore habitats and may end up seriously damaging important lake fisheries.”

Although Lake Mainit is only the fourth largest lake in the Philippines, with a total surface area of 17,060 hectares, it is the country’s deepest lake.

In a 1973 study of Lake Mainit, researcher William Lewis, Jr. found it has a maximum depth of 223 meters and a mean depth of 128 meters. In the recent MSU study, researchers found out that the lake has a maximum depth of 219 meters and mean depth of 122 meters -- a few meters short of the Lewis study. The different could be traced to siltation.

Mr. Lewis reported that the lake lies 27 meters above sea level while the more recent MSU-Naawan report showed that the lake lies 21 meters above sea level.

Towering mountains surround this lake. On the west side, the lake is separated from the Mindanao Sea by mountains as high as 600 meters. On the east side, the lake is flanked by mountains as high as 1,000 meters.

Lake Mainit is a highly productive wetland ecosystem. In a 1980-1981 study called “Fisheries yields and morphoedaphic index of Lake Mainit,” researchers headed by Daniel Pauly found 37 species of fish at the lake. However, in a 2007-2008 study, researchers from MSU found 41 species of fish.

Although the MSU researchers found more species, 13 species found by Mr. Pauly’s group were not on the list of the university-based researchers. (BusinessWorld)

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