Interactive Map 1. Map showing the selected river system darining into the Manila Bay
The lake’s watershed area of 3,820 square kilometers straddles the whole provinces of Rizal and Laguna, and some towns in Batangas, Cavite, Quezon and cities in Metro Manila. Twenty-one (21) major tributary river systems flow into the lake aside from other relatively small rivers and streams (Tongson, E. T. et al., 2012). The lake’s only outlet is the Napindan Channel which is connected to Manila Bay via the Pasig River. Seawater backflow has been a natural phenomenon in the lake and it took place in some years in the past. This happens in the lake not every year but occasionally in summer months whenever the lake level is lower than in Manila Bay. As the Pasig River reverses its flow during the entry of saltwater due to the effect of tidal fluctuation in Manila Bay, the salinity of the water in the lake increases.
As a multi use water resource, Laguna Bay is used as source of irrigation water, industrial cooling water, hydroelectric power generation, transport route, source of animal feed, a venue for recreation, source of fish supply and source of domestic water supply. The National Statistics Office (NSO) reported that as of 2010, the total population around the lake was about 15 million. To ensure the viability of this vital resource, support is needed from the various lake stakeholders and other parties interested in its sustainable use. Likewise, proper management of the lake and its watershed areas must be intensified and sustained for environmentally sound resources conservation.
From 1975 to 1977, a study was jointly undertaken by the World Health Organization (WHO) and the Laguna Lake Development Authority (LLDA) which included benchmarking of important water parameters and environmental indicators through the conduct of a Comprehensive Water Quality Management Program of Laguna Bay. Realizing the usefulness of having available water quality information on Laguna de Bay and its tributary rivers, LLDA has continuously implemented its water quality monitoring program since the 1970’s with the following objectives:
- To accurately assess the suitability of the lake for all its present and intended beneficial uses, and
- To evaluate the impacts of development activities on the lake’s water quality that will serve as important criteria for environmental planning and management.
The rivers at NCR and Region III has poor water quality results. Low Dissolved Oxygen level is the result of untreated domestic and industrial waste being discharged to the river. In Metro Manila, only 18% of the population are connected to sewerage system while the remaining population relies on septic tanks inappropriately designed, thus contributing high population load in the waterways.