Laguna de Bay is the largest brackish water lake in the Philippines with a total surface area of 900 km2. This is followed by Lake Lanao in Mindanao with a total surface area of 34,700 hectares.

Laguna de Bay is home for various species of plants and animals. About 48 percent of flowering plants and ferns endemic to the Philippines are found within the lake basin.  Mt. Makiling, located between the provinces of Batangas and Laguna, has rich biodiversity with more than 2,000 species of flowering plants and ferns, 381 species of vertebrates including 45 species of reptiles, 22 species of amphibians, and 181 species of birds.

Many people living within the watershed depend on the lake for food. High commercial value fish are milk fish or bangus, tilapia, carp, thai catfish or hito, ayungin, and biya. There are about 269 species of plants, fishes, and various kinds of aquatic organisms. But the introduction of exotic or introduced species poses negative impacts on the lake ecosystem.

Water Pollution

Being at the heart of the country's urban and industrial center, Laguna de Bay is threatened by inevitable price of progress-rapid population growth, land conversion, water pollution, and over fishing.

These rivers include San Pedro and San Cristobal in Laguna; Tunasan, Marikina, and Mangangate in Metro Manila; and Sapang Baho in Rizal.

Biochemical oxygen demand (BOD) is a measure of the quantity of oxygen used by microorganisms (e.g., aerobic bacteria) in the oxidation of organic matter.  High BOD level implies high presence of microorganisms brought about by pollution.

All the 15 rivers monitored exhibit high fecal contamination exposing to health risk about 2.7 million population.