Metropolitan Manila (MM), the capital of the Philippines is located in the hydraulically complex Pasig River - Laguna de Bay - Manila Bay watershed. Manila Bay is an important economic zone, producing 35-40% of the national GDP. All MM waterways are heavily polluted and the key watercourses, the Marikina and Pasig Rivers, are biologically dead. Up to 75% of pollution is caused by domestic sewage, with the rest originating from industry. Within MM less than 15% of residents are connected to a sewerage system, and most of the wastewater from sewerage and septage is discharged without treatment.