Sri Lanka has 103 natural river basins with a total length of around 4,500 kilometers (UNESCO and MoAIMD 2006). The Mahaweli River, which is 335 kilometers long and covers 10,448 square kilometers, is the largest river in the nation (MENR and UNEP 2009). There are also a large number of reservoirs, including ancient irrigation reservoirs and newly built multi-purpose reservoirs, totaling 169,941 hectares.