A Case Study Water Pollution in Manila Bay, Philippines ABSTRACT A study to determine the dissolved oxygen (DO) and biochemical oxygen demand (BOD) concentrations in major rivers draining into Manila Bay was conducted by Filipino scientists. The study results shows that levels of DO at the surface part of the bay are better than the 5 mg/L level, while more than 50 percent of the data for DO at the bottom layer of the water column ranged from less than 1 mg/L to 3 mg/L. These results are not good for the many fish and shellfish that live and feed near the sediment water interface of the Bay. The main cause of reduced DO is the oxygen demand from the decomposition of organic materials in the Bay which come from continuous discharges of untreated or partially treated sewage and industrial wastes, illegal dumping of septic tank sludge, tank-cleaning or operational discharges from ships, urban and rural land runoff, and algal blooms. INTRODUCTION Manila Bay is an important historical, cultural and economic resource of the Philippines. Around 30 percent of the country's population resides in the Manila Bay watershed area, and contributes as much as 52.5 percent of the national GDP. An economic valuation study (2005) of the uses of Manila Bay's resources (i.e., fisheries, aquaculture, tourism and shipping), as well as the benefits derived from key habitats (i.e., mangroves, mudflats and coral reefs), revealed a total value of more than 8 billion pesos per year. This amount represents a partial assessment of the total economic value of Manila Bay. The actual total economic value is, to all accounts, larger. Such information provides assurance that the Bay is a valuable resource that must be protected and managed sustainably. It is also a warning of what could be lost if concerted actions are not taken.An initial valuation of damages to the ecosystems of Manila Bay, and the resulting social