Encompassing the last extensive patch of primary lowland rainforest in Sri Lanka, Sinharaja Forest Reserve is situated in the south-west lowland wet zone of Sri Lanka.
Covering an area of 8,864 ha and ranging from an altitude of 300 – 1,170 meters, it consists of 6,092 ha of Forest Reserve and 2,772 ha of Proposed Forest Reserve.
This narrow strip of undulating terrain encompasses a series of ridges and valleys that are crisscrossed by an intricate network of streams. Draining to both the south and north, this detailed matrix of waterways flow into the Gin River on the southern boundary of the property and Kalu River via the Napola Dola, Koskulana Ganga and Kudawa Ganga on its northern boundary.
Annual rainfall over the last 60 years has ranged from 3614 – 5006 mm with most of the precipitation during the south-west monsoon (May-July) and the north-east monsoon (November- January).
Sri Lanka is home to 830 endemic species, of which 217 trees and woody climbers are found in the low land wet zone. Of these, 139 (64%) have been recorded in the reserve including 16 rare species.
Faunal endemism is particularly high for birds with 19 (95%) of 20 species recorded in the property being endemic to Sri Lanka. Endemism among mammals and butterflies is also greater than 50%. A number of threatened, endangered and rare species occur within the reserve including: leopard (Panthera pardus), Indian elephant (Elephas maxiumus), endemic purple-faced Langur (Presbytis senex), Sri Lanka wood pigeon (Columba torringtoni), green-billed Coucal (Centropus chlororrhynchus), Sri Lanka white-headed starling (Sturnus senex), Sri Lanka blue magpie (Cissa ornate), ashy-headed babbler (Garrulax cinereifrons) and Sri Lanka broad-billed roller (Eurystomus orientalis irisi). —UNESCO