Lake Lanao
07°53'N, 124°l5'E; in the municipalities of Dansalan, Mulundo, Jaraka, Linuk, Bayong, Binidayon, Tugaya and Lanao, Lanao del Sur Province, west-central Mindanao.
34,700 ha.
Biogeographical Province:
Wetland type:
Description of site:
A large, oligotrophic, freshwater lake in the uplands of west-central Mindanao, formed by the tectonic-volcanic damming of a basin between two mountain ranges and the collapse of a large volcano. Lake Lanao is the largest lake in Mindanao and the second largest in the Philippines. The lake basin is shallowest in the north and becomes progressively deeper towards the south. There is a large area east of the two southern islands with a depth greater than l00m; the average depth is 60.3m and the maximum 112m. The lake is fed by four rivers; its only outlet, the Agus River, flows southwest into Iligan Bay via two channels, one over the Maria Cristina Falls and the other over the Cinnamon Falls. The pH values range from 6.8 to 8.9.
Climatic conditions:
Humid tropical climate with the rainfall more or less evenly distributed throughout the year (Type IV). The average annual rainfall varies from 2,864 to 2,890 mm, and the mean monthly temperatures vary between a maximum of 27.6°C and a minimum of 22.2°C.
Principal vegetation:
Extensive reed-beds of Typha sp around the edges of the lake, and large areas of Eichhornia crassipes on the surface. Other common aquatic plants include Nymphaea nouchali and Vallisneria sp. Most of the surrounding areas have been cleared for agriculture but there is still some primary dipterocarp forest on the nearby Sacred Mountain, and there are patches of secondary dipterocarp forest at Wao.
Land tenure:
The lake is owned by the Local Authority; surrounding areas are partly state owned and partly private.
Conservation measures taken:
The lake has been declared a National Park and Reserve, and is under the jurisdiction of the Bureau of Forest Development. An environmental impact assessment has been carried out on the National Power Corporation's Hydro-electric Project on the Agus River.
Conservation measures proposed:
There is a proposal to conduct further environmental impact assessments of all the hydro-electric projects of the National Power Corporation on the Agus River and at Maria Cristina Falls.
Land use:
The lake serves as a reservoir for the generation of hydro-electric power on the Agus River. Other major uses include commercial and sport fishing, and outdoor recreation. The commercially important fishes are mudfish Ophicephalus striatus, tilapia Tilapia spp, goby Glossogobius giurus and cyprinids. Other species in the catches include catfish, climbing perch, plasalit, eels, the freshwater shrimp (Clarias sp, Anabas testudineus, Trichogaster sp. Anguilla sp, Macrobrachium sp), and the freshwater snails Ampullaria luzonica and Vivipara angularis. Grasslands adjacent to the lake are grazed by cattle, water buffalo and goats. There are several towns and many villages around the lake, and Mindanao State University Campus is situated here.
Possible changes in land use:
Disturbances and threats: The construction of additional spillways for the hydro-electric power station involves more dredging of river banks and destruction of riparian habitat. Logging in the water catchment area is accelerating soil erosion, and this is causing increased siltation and affecting water quality in the lake. Hunting causes considerable disturbance, and there is some pollution from insecticides and herbicides. The introduction of exotic species of fishes has undoubtedly had some negative effects on the very interesting native fish fauna.
Economic and social values: The lake supports a major fishery, and is important for recreational activities including boating, swimming and sport fishing. The Lanao Lake and Agus River system generates 70% of the electricity used by the people of Mindanao.
Fauna: Lake Lanao is of great limnological interest. The fauna includes many species of fishes and invertebrates which are endemic to the lake, and presents an outstanding opportunity for research on evolution in the Cyprinids. There are about twenty species of Cyprinidae endemic to the lake including Puntius (Barbodes) tamarus,P. baolan, P. binotatus, P. clemensi, P. diza, P. flavifucus, P. katolo, P. lanaoensis, P. lindog, P. manalak, P. sirang, P. tras, P. tumba, Cephalocampus pachychilus, Mandibularca resinus, Osphatulus trunculatus, O. palaemophagus and Strattellicypris palata. Other fishes occurring in the lake include species of Silurid, Anabantid, Anguillid, Ophiocephalid, Centrarchid and Chanid, but mans' of these have been introduced.

The lake supports large numbers of waterfowl, particularly Ardeidae, Anatidae and Rallidae. Counts have included:
over 500 bitterns Ixobrychus spp 500 egrets Egretia spp
50 Ardea purpurea 200 Porphyrio porphyrio
200 Fulica atra 100 Gallinago spp
and smaller numbers of Gallicrex cinerea and Gallinula chloropus. Mammals occurring in the area include the wild pig Sus celebensis and deer Cervus sp.
Special floral values: No information.
Research and facilities: A considerable amount of research has been undertaken on the limnology of the lake and its fish fauna, particularly by Mindanao State University College of Fisheries. A floral and faunal survey of Lake Lanao and its vicinity has been carried out by the Biology Department of the University.
References: An-Lim (1975); Frey (1974); Lewis (1974); Luther & Rzoska (1971); Tawagon (1984).
Criteria for inclusion: 1b, 1e, 2b, 2d, 3b.
Haribon Foundation, Simplicia N. Alonzo-Pasicolan and Perla M. Magsalay.