Manila Bay, a semi-enclosed estuary facing the South China Sea, is one of the best natural harbors in the world. The bay is located at the southwest portion of Luzon Island, one of the major islands in the Philippines. The Bay, 60km long, may be entered through a channel 18km wide, in which Corregidor and Caballo Islands are situated. It has a coastline of approximately 190 kilometers.
It is bordered by coastal cities and municipalities of the National Capital Region or NCR (Manila, Pasay, Parañaque, Las Piñas, and Navotas), and the coastal provinces of Bataan, Pampanga, Bulacan in Region 3, and Cavite in Region 4. Also within the watershed of Manila Bay are the non-coastal cities and municipalities of the NCR (Quezon City, Caloocan City, Makati, Pasig, Marikina, Mandaluyong, Muntinlupa, Valenzuela, Malabon, San Juan, Pateros, and Taguig), provinces of Nueva Ecija and Tarlac in Region 3, and Rizal and Laguna in Region 4.
The two main contributory areas are the Pasig and the Pampanga river basins. The Pasig River connects Manila Bay with Laguna de Bay, the largest freshwater lake in Southeast Asia. Most of the river systems in the province of Pampanga, Bulacan and Nueva Ecija drain into the Pampanga River (BFAR, 1995). Other major rivers discharging directly into Manila Bay are Talisay, Pasag, Meycauayan, Navotas-Malabon-Tullahan-Tenejeros, and Maragondon.
The tide is predominantly diurnal with an average tidal range of 1.2 meters during spring tide and 0.4 meter during neap tide. Seasonal wind systems (i.e., the monsoons) and diurnal breezes affect the current pattern especially in shallow water. The salinity of the water column is homogeneous in the dry season but increases from surface to bottom during the wet season. Median salinity at all depths is between approximately 30 and 35 parts per thousand, a little less than the open ocean.
The Manila Bay area is one of the Philippines’ major avenues that cater to a lot of economic activities for continuous growth and development ranging from shipping, industrial, commercial, fishing, aquaculture to tourism activities. With the various developments taking place along the bay, the natural environment of the area is facing various threats from different factors: over-population, pollution from land- and sea-based sources, over and illegal fishing, uncontrolled development, loss of habitats, and decreasing resources. The effects of these problems result in the significant degradation of the ecosystem and biodiversity thereby affecting the needs of all living things along the bay.
The waterways of Manila Bay also serves as the navigational lane of cargo ships and support large-scale industries, such as: oil refineries and depots, power plants, petrochemical plants, and economic zones, as well as tourism activities, which extend huge contributions to the national economy.