Green algae
The habitat surrounding at the reservoir includes marshes, the Walawe river and its tributaries, forests and grasslands. Dead trees standing in the reservoir are visual reminders of the extent of forest cover before the construction of the Udawalawe Dam. Green algae, including "Pediastrum" and "Scenedesmus" spp., and blue green algae species such as "Microsystis", occur in the reservoir. Areas of open grassland are abundant as a result of former chena farming practices. There is a plantation of teak beyond the southern boundary, below the dam, which was planted before the declaration of the park. Species recorded from the park include 94 plants, 21 fish, 12 amphibians, 33 reptiles, 184 birds (33 of which are migratory), and 43 mammals. Additionally 135 species of butterflies are among the invertebrates found in Udawalawe.