Gal Oya National Park in Sri Lanka was established in 1954 and serves as the main catchment area for Senanayake Samudraya, the largest reservoir in Sri Lanka. Senanayake Samudraya was built under the Gal Oya development project by damming the Gal Oya at Inginiyagala in 1950. An important feature of the Gal Oya National Park is its elephant herd that can be seen throughout the year. Three important herbs of the Ayurveda medicine, Triphala: Terminalia chebula, Terminalia bellirica and Emblica officinalis are amongst the notable flora of the forest. The National Park is situated 314 km from Colombo.
The vegetation of the forest is of three types: forest, shrub and grassland. The national park contains a substantial area of Savanna grasslands known as Thalawa in Sinhalese and mountainous grasslands known as Pathana. Thalawa grassland is dominated by rough grass species, Cymbopogon nardus ("Mana") and Imperata cylindrica ("Iluk"). The burnt Thalawa grasslands are known as the Damana grasslands and are used for cattle grazing by villagers.
32 terrestrial mammals have been recorded in the park. The Sri Lankan Elephant, Sri Lankan Axis Deer, Muntjac, Water Buffalo, Sri Lankan Sambar Deer, Sri Lanka Leopard, Toque Monkey and Wild Boar are among them. Included amongst the amphibian species of the park are the Mugger Crocodile and Star Tortoise. More than 150 species of birds have been recorded in Gal Oya. The Lesser Adjutant, Spot-billed Pelican and Red-faced Malkoha are some of the park's resident birds.