Geography of the Philippines Bay. Laguna de Bay, east of Manila Bay, is the largest freshwater lake in the Philippines. Several rivers have been harnessed for hydroelectric power. To protect the country's biological resources, the government has taken a first step of preparing a Biodiversity Action Plan to address conservation of threatened species. The islands are volcanic in origin, being part of the Pacific Ring of Fire, and are mostly mountainous. The highest point in the country is the peak of Mount Apo in Mindanao, which is above sea level. The second highest point can be found on Luzon at Mount Pulag, a peak
Arroyo de la Laguna Lake. With development of the valley starting in the 19th century, drainage alterations in this watershed reduced the lake to a watercourse now called the Arroyo de la Laguna. In the northern portion of the Arroyo de la Laguna catchment basin, the Tassajara Formation underlies Quaternary valley fill material. Contacts of these two formations are often indistinguishable due to similarities of physical characteristics. The prism of sediments identified as valley fill materials contains from eight to ten separate zones of sand and gravel separated by zones of silt and clay. Rapid development and other historic changes in the upper watershed