The origin of Palawan and indeed of all the Philippines is vague, but the following scenario, developed by Audrey-Charles (1981) and Holloway (1982), seems most likely. The most westerly part of the Philippines comprising at least the north Palawan and Mindoro were rifted off from the southwest China Sea marine basin. The fragments then collided with an intraoceanic wave that comprises the rest of the Philippines during the Oligocene. Holloway (1982) considers that northern Palawan and Mindoro comprised one rifted block. However there is a great difference between Palawan and Mindoro in that Mindoro lies off the continental shelf of southeast Asia, whilst Palawan now lies upon it. This maybe explained by a secondary rifting effect. Regarding the origin of southern Palawan, it seems that this area is composed of younger rocks and was added to the north Palawan block by volcanic and tectonic processes (Audley-Charles, pers.com).

Few researches confirm this postulated origin. It was explained that the southeast of the lake is a crater of an extinct volcano. North of this crater, the topography is very different from the rolling hill topography surrounding all other parts of the lake- the contours have been smoothened out to a great extent. This is best explained by the eruption of the volcano that resulted in a magma flow northwards to the river valley, overlaying the rolling hill topography. This dammed the river valley and formed a lake behind it to the west. The area immediately to the east of the lake, between it and marsh, is an extensive lava field whilst the numerous islands close to the eastern shore are composed of lava blocks. One can also speculate that the marshy area to the east was formed at the same time. Before the valley was dammed, the river flowed unhindered to the sea at Bantolan Bay. When the valley was dammed, this single surface flow was prevented and instead diffused underground through the lava field, which then reappeared as springs over a wide area to feed the marsh created in the former valley.

Introduction

The north of Palawan abounds with sites that has good ecotourism potential is often being forgotten when it comes to developmental thrust of the province. Though a major tourist destination, the most of the investors are from other provinces. Business tycoons from Metro Manila have established profitable business that is inaccessible to the local tourist. The local market is not being catered and much of the profit goes out of the local governments hands. Nearby oilfield is being managed by multinational companies and revenues go to the national government though shares for the local provincial government is beginning to flow in.

The lake has unique features that are potential for an income-generating site in the future. Not only that it has values of having an abundant ecosystem but it possesses a natural scenic beauty. The forested area around the lake is at least around 60% and home for abundant flora and fauna and at least 11 species of fish fauna were identified to inhabit the lake where two are endemic. Wild ducks have been observed to be abundant. Several brooks drain into the lake.

Lake Manguao, because of its unique features is ideal for ecotourism. Being called lake at the top of the mountain; as well as having a rich biodiversity are only some of its unique characteristics. Some of the recreational activities that the lake can offer include the following: fishing, swimming, boating, hiking, nature observation, sailing, canoeing, or bird watching. The lake itself could also serve to be site for scientist, researchers, and educational institution tours.

General Background

Palawan is a long narrow island aligned NE-SW with an area of 1.2 million hectares forming the southwesternmost part of the Philippines. A mountainous spine rising to over 2000 feet above sea level runs from almost the entire length of the island although in the north the mountains give way to low rolling hills, steep and fast flowing. There are very few extensive areas of lowland.

Lake Manguao is an irregularly shaped freshwater lake that has an approximate area of 700 hectares with depth ranging from 1-15 meter. Four major rivers directly drain into the lake. The deeper portion of the lake is characterized by muddy silt substratum with growth of benthic weeds. Pebbles and shell marl, black boulders, fine sand sharp rocks and muddy soil characterized the lakeshores (RMES-CFI, 1989).

Rocks underlie areas on the surrounding upland, hills, and mountain within the watershed limits, which was characterized as lava from the eruption of an extinct volcano. Soil in the watershed area is classified into two types namely: the Tapol clay loam and Babuyan clay loam which is predominantly brown in color.

Lake Manguao is a fresh body of water set among the low hills in northern Palawan. Water in the lake is mainly derived from the rainfall and from rivers surrounding the area. No outlet was found however draining the lake. This partly accounts from the continuous build up of soil in it.

Basically, the area has two pronounced weather condition, a tropical monsoon during the months of December to April, and northeast monsoon during May to November. Rainfall varies markedly from east to west due to the influence of the mountainous terrain. Rainfalls during the southwest monsoon and so the eastern parts in the lee of the mountains receive the least amount, which is about 1600 mm a year. As much as 5000 mm per year falls on the mountains whilst the western coast receives about 3000 mm per year.

Adjacent to the area is forestland (primary and secondary forest), which forms the most of its vegetation cover especially within the watershed area. Important plant species like molave, amugis and some Dipterocarp species are dominant in the area. Second growth forests (brushland) are result of abandoned kaingin area. These forest areas are not diverse due to the effect of slash and burn farming being practiced by the local farmers even to this date. Wetland areas are located in the eastern side. It is in the area where Lake Manuytuy is located. Cultivated land and open grassland are those areas where forest vegetation is lacking of such an amount that it is insignificant to prevent erosion. The dominant vegetation that was observed in the area is grass of various species. Interspersed with kaingin, riceland, and diversified croplands, these areas are residential and sitios.

Two sitios of two barangays are within the area of the lake, Sitio Lake Danao, and Sitio Pinangbang. Previous surveys revealed about 71 households surrounding the lake but during the recent years it was said to be increasing. Unregistered inhabitants are about 80 families. Majority of the local community belongs to the cultural group of Cuyunon and Tagbanua. Some belongs to the Cebuano, Ilonggo, and Tagalog. People in the area are quite organized and are headed by its Sitio leader.

Major impact on the natural ecosystem of the lake was based on the global climatic conditions. The province is quite safe from typhoon and natural calamities though, during the past years, heavy downpour of rains during the rainy season and drought during the long dry season was experienced.

Almost all the people are dependent on the local resources, which in time would be depleted when not properly managed. Population growth brought about by migration from other provinces results to the reutilization of available resources and in time when there is nothing more to get, it results to doing of illegal activities.

Common problems contributed by the local people are their way of farming, the slash, and burn method, which contributes to the decrease of forest cover and natural vegetation. Watershed areas are also being threatened due to shifting cultivation, illegal logging and squatting. Accelerated soil erosion, siltation, sedimentation and reduction of soil fertility results due to such activities.

This encroachment on natural ecosystem tends to disrupt the regeneration of the forest. Foreign species such as Tilapia nilotica are introduced into the area that outnumbered the existing endemic species.

Though at present, most of the clearance is confined to the gentler slopes around the bays, but there is a threat that forest on steeper grounds would be cleared as more settlers are coming in. If the catchments are to be preserved, there is an urgent need to develop appropriate farming methods and to limit clearance on gentler slopes. The clearance practiced around the lake is not kaingin in its strictest sense in that plots are cleared by settlers only around their permanent residences and then these plots maybe rotated with crops or left fallow for certain periods.

It was observed, based on the assessment of the DENR that the water level has increased to about 5 meters during the last 10 years. Around the lake is a population of about 80 families. (registered is only 70). The community around the lake is dependent on the local resources, basically fishing, and agriculture.