Laguna de Bay
Location:	14°11'-14°32'N, 121°03'-121°29'E; 10 km southeast of Metro Manila, bounded in the north by Rizal Province and in the south by Laguna Province, Luzon.
Area:	91,136 ha. The area of the watershed excluding the lake is 382,000 ha.
Altitude:	2m.
Biogeographical Province:	4.26.12.
Wetland type:	11 & 14.
Description of site:	The largest lake in the Philippines, with a shoreline of about 220 km and a total volume of 3.2 billion cubic metres. A shallow freshwater lake, formerly an extension of Manila Bay which was cut off at its northern end by slight arching that took place along the eastern shore of the Bay. The lake is naturally eutrophic and highly productive. Increasing enrichment in terms of plant nutrients such as nitrogen and phosphorus has been caused by human activities in the watershed. The lake is surrounded by low-lying alluvial plains which are often inundated during heavy rainfall. The lake drains through a single outlet, the Napindan Channel, which joins the Marikina River seven km downstream to form the Pasig River. The latter flows into Manila Bay. The mean depth of the lake is 2.5-3.0m and the maximum 6.5m. The pH varies from 7.6 during the cool months to 10 at the peak of algal bloom in mid summer; the average is about 8.5. The water is relatively turbid, and has an average dissolved oxygen of 10.5 p.p.m. Wind action can cause severe turbidity due to suspension of bottom sediments, particularly during typhoons. At the end of the dry season, the level of the lake often falls below that of Manila Bay, allowing sea water to flow into the lake at high tide. However, a hydraulic control structure has recently been constructed on the Napindan Channel and this backflow no longer occurs. The lake reaches its maximum level between September and November, and then falls by an average of 1.7m to its lowest level in May or June. The lake is fed by 21 small rivers and streams, and the total inflow from the watershed is capable of flushing the entire lake once a year.
Climatic conditions:	Most of the lake has a tropical climate with a pronounced dry season from November to April and a pronounced rainy season for the remainder of the year (Type I), but in the extreme east, the rainfall is more evenly distributed throughout the year (Type IV). The average annual rainfall varies from about 1,600 mm in the west to 3,200 mm in the mountainous northeastern part of the watershed. The mean annual temperature is 27°C; mean monthly temperatures range from 25°C to 29.5°C, and the extremes are 16°C and 40°C. The mean annual relative humidity 76%.
Principal vegetation:	Large areas of Eichhornia crassipes in the lake and along quiet stretches of its tributaries. At its most prolific, the Eichhornia can cover as much as 5% of the lake's surface. There is some emergent marsh vegetation on the southeastern shore of the lake and in the Siniloan area, dominated by species of Phragmites and Typha. Other aquatic plants include Nymphaea sp, Hydrilla verticillata, Ipomoea reptans and filamentous algae. The dominant natural vegetation is surrounding areas is Imperata cylindrica and Saccharum spontaneoum, but most of the land is cultivated for crops such as rice, corn, sugar cane, root vegetables, cacao, coffee and coconuts.
Land tenure:	The lake is state owned (public water); surrounding areas are privately owned.
Conservation measures taken:	No protected areas have been established. The Haribon Foundation has launched a "Save the Lake Movement", and a considerable amount of mass media coverage has been given to the problems facing the lake. As a result of pressure from the Haribon Foundation, the Rizal Cement Factory, which previously dumped its effluent into the lake at Binangonan, has been closed.
Conservation measures proposed:	Various proposal have been made in the past for environmental improvement and the creation of fish sanctuaries to prevent further depletion of the fish stocks. In the early l980s, the Laguna Lake Development Authority produced a Lake Fishery Zoning and Management Plan, the basic aim of which was to reduce the area of fish pens to 21,000 ha, but it seems that this plan was never implemented. Davies et al. (1986) have recently summarized the problems facing the lake ecosystem and have made a number of recommendations on fish pens, the use of the lake for irrigation and human water supply, and future research.
Land use:	Open-water fishing has been carried out in the lake for a considerable time. In the l960s, the commercial fishery consisted of finfish, shrimps, clams and snails. In 1961-1964, the yearly catch of fish averaged 80,000-82,000 metric tonnes and that of shrimps and molluscs about 240,000 metric tonnes. However, with the introduction of motor boats and widespread use of nets with very small mesh, fish stocks were seriously depleted, and by 1968 the annual harvest of fish had fallen to 39,000 metric tonnes. Most of the fish caught were of low market value and were used for animal feed. In 1970, the Laguna Lake Development Authority pioneered a new type of fish culture using fish pens to rear milkfish (Chanos chanos) and other species for human consumption. This proved to be very successful and there was a rapid proliferation of fish pens throughout the lake. By 1983, 31,000 ha of the lake were covered by fish pens, and by 1987, about 70% of the lake surface had been enclosed. Other uses include the raising of ducks and poultry, transportation, and irrigation. Land use in the watershed is varied; the northwestern portion is highly urbanized and industrialized, while the southern portion is mostly agricultural with rice production, livestock, poultry and duck-raising as the main activities. In the entire Laguna Lake basin, there are 43,800 ha of rice paddies, 11,900 ha of varied crops, 69,900 ha of fruit trees, 211,100 ha of forest, 141,900 ha of grassland and scrub, 4,000 ha of wetlands and 25,200 ha of developed land.
Possible changes in land use:	Fishpond operations are being encouraged in the surrounding areas to increase the supply of fish products for Metro Manila. As the demand for drinking water for Manila begins to exceed river sources, some thought is being given to the development of the lake for human water supply. This would require a programme of strict pollution control to improve water quality, which would in turn improve productivity and ensure the long-term sustainability of the lake system.
Disturbances and threats:	The rapid proliferation of fish pens and intensive aquaculture have produced a number of serious problems including slower rates of fish growth and lower yields. The yield of fish from the fish pens was halved between 1973 and 1982, and the open water fishery showed a 46% decline in yield in the same period. Because of the poorer fish harvests, the fish pen operators have resorted to supplementary feeding and this has had a detrimental effect on water quality. Furthermore, the pens have rendered access to open water fishing areas difficult, and have reduced water circulation, which has favoured the spread of water hyacinth. The rapid development of the lake region has resulted in high levels of pollution from human, industrial and agricultural sources. The dumping of waste from plastic and textile factories and poultry farms has been especially harmful. The most serious pollutants are the heavy metals, lead, mercury and cadmium, and certain pesticides widely used on neighbouring agricultural land. Other threats to the lake system include the control of water levels for agricultural, domestic and industrial purposes, and extensive reclamation works on the foreshore for development of industrial estates, residential estates and recreation facilities. Deforestation in the water catchment area has resulted in severe soil erosion and increased siltation in the lake. The closure of Napindan Channel with a hydraulic control structure has prevented the inflow of sea water from Manila Bay, and this has resulted in increased turbidity of the lake waters and a subsequent increase in algal blooms.
Economic and social values:	Laguna de Bay is of outstanding importance for its fisheries production, and could provide a very substantial source of fresh water for Metro Manila. However, unless effective measures are taken in the near future to curb over-exploitation and reduce levels of pollution, there is a real danger that these valuable natural resources will be destroyed.
Fauna:	The lake is known to support at least 23 native species of fishes belonging to 16 families, and many more species have been introduced. Commercially important fishes include white goby, mudfish, ayungin, milkfish, catfish, kanduli, the tilapias, common carp and plasalit (Glossogobius giurus, Ophicephalus striatus, Therapon plumbeus, Chanos chanos, Clarias sp, Anus rnanilensis, Tilapia mossambica, T. nilotica, Cyprinus carpio and Trichogaster sp). The freshwater prawn Macrobrachium sp is also harvested commercially. A wide variety of waterfowl occur, the commoner species including Ixobrychus sinensis, I. cinnamomeus, Ardea cinerea, Rallus mirificus (a species endemic to the Philippines), Porphyrio porphynio, Fulica ama, Himantopus himantopus and Sterna albitrons.
Special floral values:	None known.
Research and facilities:	A considerable amount of limnological and fisheries research has been carried out, and a continuous research programme has been developed to study the lake waters and their resources, isolate major problems and seek their solutions. Numerous studies have been conducted by the Laguna Lake Development Authority, Bureau of Forest Development, Forest Research Institute, University of the Philippines (Diliman and Los Banos), PCARRD, IRRI, National Museum and SEAFDEC. The lake exhibits an accelerated geological ageing which is of outstanding ecological interest.
References:	Alonzo-Pasicolan (1987); Bureau of Fisheries and Aquatic Resources (1984-85); Davies et al. (1986); Laguna Lake Development Authority (1978); Lonsigan (1985); Luther & Rzoska (1971); National Water Resources Council (l983b).
Criteria for inclusion:	1e, 2d, 3b.
Source:	Simplicia N. Alonzo-Pasicolan and Haribon Foundation.