Which river is Sri Lanka's longest?

The Mahaweli River is Sri Lanka’s longest river, extending about 335 kilometres.

Known in Sinhala as the Mahaweli Ganga, a name meaning “Great Sandy River,” it rises in Sri Lanka’s central highlands, with its source associated with Horton Plains National Park. The river then flows toward the northeast and reaches the Bay of Bengal through Trincomalee Bay, one of the island’s finest natural deep-water harbours.

Its importance goes well beyond its length. The Mahaweli drainage basin covers about 10,448 square kilometres, nearly one-fifth of Sri Lanka’s area and the largest river basin in the country. Dams and reservoirs built under the Mahaweli Development Programme support irrigation in the dry zone and generate hydroelectricity.

The Walawe, Kalu and Kelani are also major Sri Lankan rivers, so they can seem plausible in a multiple-choice question. They are shorter, however. Another useful distinction is that the Mahaweli is not merely the longest river: its basin is also Sri Lanka’s largest, making it central to the island’s agriculture, water management and power supply.