Laguna de Bay

Islands

Known lake islands include Talim, the largest and most populated island on the lake;^[13] Calamba Island, which is completely occupied by the Wonder Island resort in Calamba, Laguna;^[13] Cielito Lindo, a privately owned island off the coast of mainland Cardona, Rizal;^[13][14] Malahi Island which used to be the site of Maligi Island military reservation, near the southern tip of Talim;^[13][15] the nearby islands of Bonga and Pihan, also in Cardona; and Bay Island off the coast of Bay, Laguna, which is closely associated with the precolonial crocodile-deity myths of that town.^[4]

Tributaries

The lake is fed by 45,000 km² (17,000 sq mi) of catchment areas and its 21 major tributaries. Among these are the Pagsanjan River which is the source of 35% of the Lake's water, the Santa Cruz River which is the source of 15% of the Lake's water, the Marikina River (through the Manggahan Floodway), the Mangangate River, the Tunasan River, the San Pedro River, the Cabuyao River, the San Cristobal River, the San Juan River, the Bay, Calo and Maitem rivers in Bay, the Molawin, Dampalit and Pele rivers in Los Baños, the Pangil River, the Tanay River, the Morong River, the Siniloan River and the Sapang Baho River.^{[8] [16]}

The lake is primarily drained through the Pasig River, which is technically a tidal estuary instead of a unidirectional "river."

Invasive species

At least 18 fish species are known from Laguna de Bay; none are strictly endemic to the lake, but 3 are endemic to the Philippines: Gobiopterus lacustris, Leiopotherapon plumbeus and Zenarchopterus philippinus.^[22] Aquaculture is widespread in Laguna de Bay, but often involves non-native species.^[23] Some of these, such as the janitor fish, clown knifefish, Thai catfish, and blackchin tilapia,^[24] have escaped and have become invasive species, representing a threat to native fish.^[25]

Pollution

Government data showed that about 60% of the estimated 8.4 million people residing in the Laguna de Bay Region discharge their solid and liquid wastes indirectly to the lake through its tributaries. A large percentage of these wastes are mainly agricultural while the rest are either domestic or industrial^[26] According to DENR (1997), domestic and industrial wastes contribute almost equally at 30% each. Meanwhile, agricultural waste takes up the remaining 40%. In a recent sensitivity waste load model ran by the Laguna Lake Development Authority's (LLDA) Integrated Water Resources Management (IWRM) division, it revealed that 70% of biochemical oxygen demand (BOD) loadings came from households, 19% from industries, and 11% came from land run-off or erosion (LLDA, 2005).

As far as industries and factories are concerned, there are about 1,481 and an increase is expected.^[10] Of the said figure, about 695 have wastewater treatment facilities. Despite this, the lake is absorbing huge amounts of pollution from these industries in the form of discharges of industrial cooling water, toxic spills from barges and transport operations, and hazardous chemicals like lead, mercury, aluminum and cyanide.^[27] Based on the said figure, 65% are classified as "pollutive" industries.

The hastened agricultural modernization throughout the region took its toll on the lake. This paved the way for massive and intensified use of chemical based fertilizers and pesticides whose residues eventually found their way to the lake basin. These chemicals induce rapid algal growth in the area that depletes oxygen levels in the water. Hence, oxygen available to the lake is being used up thereby depleting the available oxygen for the fish, causing massive fish kills.^[28] A 2012 study found excessive pesticide use largely attributed to overapplication of pesticides close to waterways.^[29]

As far as domestic wastes are concerned, around 10% of the 4,100 metric tons (4,000 long tons; 4,500 short tons) of waste generated by residents of Metro Manila is dumped into the lake, causing siltation of the lake. As reported by the now defunct Metropolitan Manila Waterworks and Sewerage System (MWSS), only 15% of the residents in the area have an effective waste disposal system. Moreover, around 85% of the families living along the shoreline do not have toilets and/or septic tanks.^[21][28]

In 2018 a survey on Microplastics were conducted by researchers from the Polytechnic University of the Philippines, and have found out that the Laguna de Bay is heavily polluted with microplastics. The study involved three (3) barangays and these are Napindan, San Isidro, and Sampiruhan. Among the barangays, Sampiruhan in Calamba, Laguna has the most microplastics, with a median of 15 ranging from 11 to 24 microplastics per 1000 liters of lake water.^[30] The data from the conducted survey is available in Mendeley Data.^[31]

Overfishing

On January 29, 2008, the Mamamayan Para sa Pagpapanatili ng Pagpapaunlad ng Lawa ng Laguna (Mapagpala) accused the Laguna Lake Development Authority (LLDA) of the deterioration of Laguna de Bay due to multiplication of fish pens beyond the allowable limit.^[32]

Manggahan floodway

This section is an excerpt from Manggahan Floodway.[edit]

The Manggahan Floodway is an artificially constructed waterway in Metro Manila, Philippines. The floodway was built in 1986,^[33] at a cost of 1.1 billion pesos, in order to reduce flooding along the Pasig River during the rainy season, by diverting the peak water flows of the Marikina River to Laguna de Bay, which serves as a temporary reservoir.^[34][35] If the water level on the lake is higher than the Marikina River, the floodway's flow can be reversed.

By design, the Manggahan Floodway is capable of handling 2,400 cubic meters per second of water flow, although the actual flow is about 2,000 cubic meters per second. To complement the floodway, the Napindan Hydraulic Control System (NHCS) was built in 1983 at the confluence of the Marikina River and the Napindan Channel of the Pasig River to regulate the tidal flow of saline water between Manila Bay and the lake, and to prevent the intrusion of polluted water into the lake.^[34]

It has a fully gated diversion dam at its head and was designed with a width of 260 meters (850 ft). Over 40,000 households are situated along the floodway's banks^[36] and these shoreline slums have reduced its effective width to 220 meters (720 ft). Kangkong is cultivated extensively in the floodway as well.

The Manggahan Floodway was supposed to function together with the proposed Paranaque Spillway Project, a spillway that would direct flood waters from Laguna de Bay to Manila Bay. However the spillway project was cancelled in 1977 due to budget issues.^{[37][38]: 61} Since the onslaught of 2009's Typhoon Ketsana (Ondoy), and consistently-reoccurring flooding in the metropolis, the Paranaque Spillway project is being revived,^[39] together with the proposed Marikina Dam.^[40]

Laguna Lakeshore Expressway Dike

In 1997, a proposed 32.5-kilometer (20.2 mi) limited access highway, the Laguna de Bay Coastal Road, was planned by the joint venture of the Philippine National Construction Corporation, DMCI, John Laing, Filinvest, and the Citra Metro Manila Tollways Corporation (CMMTC; now SMC Skyway Corporation). The alignment would have run between Taytay, Rizal and San Pedro, Laguna.^[41][42]

The project was initially conceived as a public-private partnership project, but the project was not successful in receiving bids.^[48] The project would later be revised as an untolled highway, known as the Laguna Lakeshore Road Network (LLRN) under a new proposal. The highway project has a total length of about 37.4 kilometers (km) expressway from Lower Bicutan in NCR to Calamba in Laguna Province, consisting of (i) 11.7 km long viaduct from Lower Bicutan to Tunasan; and (ii) 25.7 km long combination of shoreline viaduct and embankment from Tunasan to Calamba. The expressway will be an access-controlled road with eight interchanges, with an access road at each interchange to connect to the existing road networks.^[49] The Export-Import Bank of Korea-Economic Development Cooperation Fund (KEXIM-EDCF) and the Asian Development Bank (ADB) will jointly finance the project.^[50]

Eastbay Submarine Pipeline and Pakil Water Treatment Plant Projects

The Manila Water began laying down in 2021 two high density polyethylene (HDPE) underground and 21 km submarine pipes from Binangonan, Cardona, Morong, and Pililla to expand their services under the East Bay Phase 1 Project. These two pipes once completed will deliver 50 million liters per day (MLD) to the said area. The environmental impact of the project was worked on by the University of the Philippines Los Baños.^[51][52]

East Bay Phase 2 Project will involve construction of a water treatment plant (WTP) at Bgy. Kabulusan, Pakil, Laguna beginning 2023. The WTP once completed will produce 200 MLD for the Metro Manila East Zone through the submarine pipeline under the lake.^[53][54]

Clean Water Act

The technical aspect regarding the quality of wastewater is given in DENR Administrative Order 1990–35. The order defines the critical water parameters' value versus the classification of the body of water (e.g., lake or river). Discharge permits are issued by the LLDA only if the wastewater being discharged complies with the said order.^[57]

According to the Clean Water Act of 2004, the DENR (through the LLDA) shall implement a wastewater charge system in all management areas including the Laguna Lake region and Regional Industrial Centers through the collection of wastewater charges/fees. The system shall be established on the basis of payment to the government for discharging wastewater into the water bodies. Wastewater charges shall be established taking into consideration the following: a) to provide strong economic inducement for polluters to modify their production or management processes or to invest in pollution control technology in order to reduce the amount of water pollutants generated; b) to cover the cost of administering water quality management or improvement programs, including the cost of administering the discharge permitting and water pollution charge system; c) reflect damages caused by water pollution on the surrounding environment, including the cost of rehabilitation; d) type of pollutant; e) classification of the receiving water body; and f) other special attributes of the water body.^[58]

Integrated Coastal Ecosystem Conservation and Adaptive Management

CECAM is a 5-year research cooperation between Japanese and Filipino scientists. Seven monitoring instruments are being used as part of the Continuous and Comprehensive Monitoring System (CCMS) provided by the Japanese government.^[59]