Baños, the Pangil River, the Tanay River, the Morong River, the Siniloan River and the Sapang Baho River. The lake is primarily drained through the Pasig River, which is technically a tidal estuary instead of a unidirectional "river." Uses The lake is a multipurpose resource, used for fishery, transportation, irrigation of agricultural lands, power generation, and as a reservoir for regional flood management, among other things. The lake has been used as a navigation lane for passenger boats since the Spanish colonial era. It is also used as a source of water for the Kalayaan Pumped-Storage Hydroelectric Project in Kalayaan, Laguna. Other uses include fishery, aquaculture, recreation, food support for the growing duck industry, irrigation and a "virtual" cistern for domestic, agricultural, and industrial effluents. Environmental issues Because of its importance in the development of the Laguna de Bay Region, unlike other lakes in the country, its water quality and general condition are closely monitored. This important water resource has been greatly affected by development pressures like population growth, rapid industrialization, and resources allocation. Invasive species At least 18 fish species are known from Laguna de Bay; none are strictly endemic to the lake, but 3 are endemic to the Philippines: Gobiopterus lacustris, Leiopotherapon plumbeus and Zenarchopterus philippinus. Aquaculture is widespread in Laguna de Bay, but often involves non-native species. Some of these have escaped and have become invasive species, representing a threat to the native fish. Pollution Government data showed that about 60% of the estimated 8.4 million people residing in the Laguna de Bay Region discharge their solid and liquid wastes indirectly to the lake through its tributaries. A large percentage of these wastes are mainly agricultural while the rest are either domestic or industrial According to DENR (1997), domestic and industrial wastes contribute almost equally at 30% each. Meanwhile, agricultural wastes take up the remaining 40%. In a recent sensitivity waste load model ran by the Laguna Lake Development Authority's (LLDA) Integrated Water Resources Management (IWRM) division, it revealed that 70% of biochemical oxygen demand (BOD) loadings came from households, 19% from industries, and 11% came from land run-off or erosion (LLDA, 2005). As far as industries and factories are concerned, there are about 1,481 and increase is expected. Of the said figure, about 695 have wastewater treatment facilities. Despite this, the lake is absorbing huge amounts of pollution from these industries in the forms of discharges