Laguna de Bay (also known as Laguna Lake), the country’s largest freshwater lake, with an area of 90,000 hectares and average depth of 2.5 meters, has an estimated 3.2 trillion liters of water. The water of the lake is supplied by 24 tributary rivers with the Marikina River, Pagsanjan River, and Sta. Cruz River as main contributors. The only outlet of the lake to Manila Bay is the Napindan Channel through the 24-kilometer long Pasig River. During the dry season when the water level in the lake is below sea level, the Pasig River backflows into the lake making it partly saline.
According to the Laguna Lake Development Authority, the water quality of Laguna de Bay is classified as Class C Water of the Department of Environment and Natural Resources (DENR) which is suitable for fisheries and recreation. The water of the lake is not fit for drinking by humans as is without treatment to make it Class A (potable water). The average coliform (fecal bacteria) count of less than 3,000 MPN (most probable number) and inorganic phosphorus level of 5 milligrams per liter of the untreated lake water need to be reduced to 50 MPN and 0.1 mg/l, respectively, to make it Class A, among other criteria.
About 15 million people live on the Laguna de Bay basin. More than 4 million people living on the lake’s shoreline have no sewage facilities. Domestic wastes (solid and liquid) comprise 80% of the lake’s pollution. In addition to the bacterial and mineral pollutants, a recent study by scientists of the University of the Philippines Los Baños showed that the water of the lake has high concentrations of endocrine-disrupting compounds (EDCs) such as estroge