The land of lakes
Wilpattu National Park, the largest in Sri Lanka at 1,317 square kilometers, derives its name from the Sinhalese "Villu-pattu," meaning "Land of Lakes". This name refers to the park's most distinctive feature: a complex of around 60 natural, shallow, rain-fed depressions known as villus. These are not true lakes as they generally lack inlets or outlets, they are self-contained basins lined with clay that collect and hold monsoon rainwater. The size of these villus fluctuates dramatically, ranging from under 10 hectares to over 160 hectares when full.
The park's hydrology is dictated by a distinct seasonal pattern. The primary rainy season, driven by the northeast monsoon, occurs from September to December, with an inter-monsoon period bringing more rain in March and April. During these times, the villus swell, creating vast aquatic habitats. Conversely, a pronounced dry season from May to early September causes many of the smaller villus to shrink and disappear completely, leaving behind cracked clay beds. This cycle of inundation and desiccation is fundamental to the park's ecology.
Geochemical fingerprints
The water within each villu possesses a unique chemical signature, a direct result of the local geology. The park's western areas sit atop Miocene-era Jaffna limestone, while other regions are part of the Vijayan series, a complex of metamorphic rocks like granitic gneiss. As rainwater percolates through the soil and interacts with this underlying rock, it dissolves different minerals.
This process creates a spectrum of water chemistries across the park. While many villus are freshwater, some are distinctly brackish or saline. For example, Kokkare Villu and Lunu Wila are known for their high salinity. Studies have documented significant disparities in pH, total phosphate concentration, and salinity among villus, even those in close proximity. These differing chemical compositions mean that each villu functions as a kind of aquatic island, with conditions that support a specialized community of microorganisms and invertebrates adapted to its specific water type.
An ecological hub
The seasonal availability of water and the unique chemistry of each villu are the drivers of life in Wilpattu. The fluctuating water levels create a dynamic gradient of vegetation, from grasslands on the villu beds that flood during the wet season to dense dry evergreen forests on higher ground. Important tree species include Palu (Manilkara hexandra), whose fruit is a favorite of sloth bears, and Ebony (Diospyros ebenum).
This mosaic of habitats supports 31 mammal species. During the dry season, the remaining villus are important water sources, concentrating wildlife and offering prime viewing opportunities. The park is a stronghold for the Sri Lankan leopard (Panthera pardus kotiya), with population density estimated at 18 individuals per 100 square kilometers. Sri Lankan elephants (Elephas maximus maximus), sloth bears (Melursus ursinus inornatus), and sambar deer are also regularly seen. The villus are also important for reptiles like the Mugger crocodile and numerous resident and migratory birds, including the Painted Stork and Spoonbill.