The La Mesa watershed is a government property titled under the MWSS and commissioned in 1929. It straddles the boundaries of Quezon City, Caloocan City, and Municipality of Montalban and the provinces of Bulacan, and Rizal. It houses the filtration plant that distributes water to 5 cities and 32 municipalities or about 12 million residents in Metro Manila. It is also the last forest of its size in the metropolis.

The concentric expansion of human population in Metro Manila affected the La Mesa Watershed. The recurring water shortage in Metro Manila has been the primary concern of the Metropolitan Waterworks and Sewerage System (MWSS) which was aggravated by the severe droughts starting in the late 1980’s. Also, the high percentage of losses through leaks, improper use of facilities, and thefts compounded the situation. Likewise, many of the unemployed flocked into the watershed converting a sizable area into croplands. Due to the inadequacy of watershed protection, the former natural forest cover dwindled resulting to the invasion of grass plant community types in La Mesa.

A few years back MWSS considered three options to increase the water supply. First, by implementing the Angat Water Supply Optimization Project (AWSOP); secondly, the Umiray Transbasin Project which was recently completed, and thirdly, tapping water from the Laguna Lake and treat it before distribution. Only the first two options were made operational. Even with the additional sources of surface water, MWSS still faced the daunting task of adequately storing water from Angat and Umiray. Increasing the storage capacity of the La Mesa reservoir, the largest in Metro Manila, was seriously considered. A proposal to conduct a feasibility study for the expansion of the storage capacity of the La Mesa Reservoir costing about P15.2 million was submitted in December 1989. The MWSS top management believed that raising the spillway dam was the best approach. Aside from this, the necessity to reduce erosion and sediment transport was also recognized and called for massive reforestation in the watershed areas as this is the key to soil and water conservation.

As the watershed degradation became more alarming the government contracted the services of the Manila Seedling Bank Foundation, Inc. starting in 1978 to undertake massive reforestation in La Mesa until 1983. Again, after the pull-out of the Manila Seedling bank and due to inadequate protection a significant number of planted forest trees were illegally harvested and more areas were converted again into agricultural croplands. The unmanaged human activities especially squatting and croplands cultivation are causing severe watershed degradation. There is an estimated 1,000 to 1,500 hectares denuded areas inside the watershed that causes soil erosion and silt deposition in the reservoir as a result of intensive cultivation and other types of agricultural use. If not protected, it will eventually be totally devoid of trees and be converted into a settlement area just like the adjacent Montalban Watershed.

In response, Bantay Kalikasan of the ABS-CBN Foundation, Inc. came into the picture and started a reforestation program in the 2,700-hectare La Mesa Watershed Area in June 21, 1999.By rehabilitating and managing the La Mesa watershed as a nature park, the following values would be enhanced: a) watershed protection, b) education, c) recreation-aesthetics, d) wildlife, e) research, to name a few. It was designed to serve as the natural laboratory of the general public and interested educational institutions and envisioned to heighten environmental awareness. Ultimately, the plan was to replicate learning from the La Mesa in other similar critical watersheds in the country.