Laguna de Bay

Laguna de Bay is the largest lake in the Philippines.

It is a massive freshwater body located on Luzon Island. The lake sits southeast of Metro Manila. It is bordered by the province of Rizal to the north and northeast. The province of Laguna sits to the south, east, west, and southwest. Metro Manila borders the lake to the northwest. This lake is a vital resource for millions of people. It supports fisheries, agriculture, and domestic needs.

The lake's unique shape and structure come from volcanic history. It is shaped like a crow's foot. This shape occurs because two peninsulas fill a large volcanic caldera. This area is called the Laguna Caldera.

Scientists believe two major eruptions formed this caldera. These eruptions happened around 1 million years ago and again between 27,000 and 29,000 years ago. The middle part of the lake sits within this caldera. A large island named Talim sits in the center of the lake.

Water moves through the lake in a specific cycle. The lake is fed by 21 major tributaries. These include the Pagsanjan River and the Santa Cruz River. The Pagsanjan River provides 35% of the lake's water. The Santa Cruz River provides 15% of the water. Other rivers like the Marikina River also contribute through the Manggahan Floodway. The lake is quite shallow with an average depth of about 2.5 meters. Its surface area is between 911 and 949 square kilometers. The excess water drains out through the Pasig River. This river is technically a tidal estuary. It carries the water to Manila Bay.

The name of the lake has a long and complex history. In the pre-Hispanic era, it was known as Puliran Kasumuran. Later, it was called Pulilan. The name Laguna de Bay comes from the lakeshore town of Bay. The name Bay likely comes from the Tagalog word bahayan, meaning settlement. During the American administration, English influence caused some confusion. People mistakenly used the English word "bay" to refer to the town. This led to mispronunciations. The Spanish word laguna can mean both a lagoon and a freshwater lake. This is why some people call it Laguna Lake. However, the "Laguna" in that name refers to the province of Laguna.

Laguna de Bay serves many important economic purposes. It is a primary source of freshwater fish for the country. It is also used for aquaculture and supporting the duck industry. People use the water for irrigation to grow crops. The lake helps with power generation through the Kalayaan Pumped-Storage Hydroelectric Project. It also serves as a reservoir for regional flood management. Since the Spanish colonial era, it has been a navigation lane for passenger boats.

In 2023, a new water treatment plant was opened in Muntinlupa City. This plant can process 150 million liters of drinking water a day.

Despite its importance, the lake faces serious environmental challenges. Population growth and rapid industrialization put pressure on the water. About 60% of the 8.4 million people in the region discharge waste into the lake. This waste comes from three main sources. Agricultural waste makes up 40% of the load. Domestic waste and industrial waste each contribute about 30%. Some industries discharge toxic chemicals like lead, mercury, aluminum, and cyanide.

Additionally, chemical fertilizers from farms cause rapid algal growth. This process uses up the oxygen in the water. This can lead to massive fish kills.

Invasive species also threaten the lake's ecosystem. There are at least 18 known fish species in the lake. Some fish are endemic to the Philippines, such as Gobiopterus lacustris. However, non-native species have escaped into the wild. These include the janitor fish, clown knifefish, Thai catfish, and blackchin tilapia. These invasive species represent a threat to native fish populations. Researchers have also found that the lake is heavily polluted with microplastics. Studies in areas like Sampiruhan found many microplastics in the water. Protecting the water quality is essential for the people who live there.