The Mahaweli River is a 335 km (208 mi) long river, ranking as the longest river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in Sri Lanka

Sri Lanka

Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka is a country off the southern coast of the Indian subcontinent. Known until 1972 as Ceylon , Sri Lanka is an island surrounded by the Indian Ocean, the Gulf of Mannar and the Palk Strait, and lies in the vicinity of India and the...

. Its drainage basin

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 is the largest in the country, and covers almost one-fifth of the total area of the island. The river reaches the Bay of Bengal

Bay of Bengal

The Bay of Bengal , the largest bay in the world, forms the northeastern part of the Indian Ocean. It resembles a triangle in shape, and is bordered mostly by the Eastern Coast of India, southern coast of Bangladesh and Sri Lanka to the west and Burma and the Andaman and Nicobar Islands to the...

 on the southwestern side of Trincomalee

Trincomalee

Trincomalee is a port city in Eastern Province, Sri Lanka and lies on the east coast of the island, about 113 miles south of Jaffna. It has a population of approximately 100,000 . The city is built on a peninsula, which divides the inner and outer harbours. Overlooking the Kottiyar Bay,...

 Bay. The bay includes the first of a number submarine canyon

Submarine canyon

A submarine canyon is a steep-sided valley on the sea floor of the continental slope. Many submarine canyons are found as extensions to large rivers; however there are some that have no such association. Canyons cutting the continental slopes have been found at depths greater than 2 km below sea...

s, making Trincomalee one of the finest deep-sea harbor

Harbor

A harbor or harbour , or haven, is a place where ships, boats, and barges can seek shelter from stormy weather, or else are stored for future use. Harbors can be natural or artificial...

s in the world. The river and its tributaries are dam

Dam

A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...

med at several locations to allow irrigation

Irrigation

Irrigation may be defined as the science of artificial application of water to the land or soil. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and revegetation of disturbed soils in dry areas and during periods of inadequate rainfall...

 in the dry zone, with almost 1000 square kilometre of land irrigated. Production of hydroelectricity

Hydroelectricity

Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 from six dams of the Mahaweli system supplies more than 40% of Sri Lanka's electricity needs. One of the many sources of the river is the Kotmale Oya

Kotmale Oya

The Kotmale River is a tributary of the Mahaweli River, and is the fourth longest river in Sri Lanka. The river begins as the Agra Oya, in the Horton Plains in the Central Highlands. The Central Plains have an annual rainfall of between 125 and 200 inches a year. The river is about 70km long and...

.

Branches

• Kotmale Oya
  Kotmale Oya
  The Kotmale River is a tributary of the Mahaweli River, and is the fourth longest river in Sri Lanka. The river begins as the Agra Oya, in the Horton Plains in the Central Highlands. The Central Plains have an annual rainfall of between 125 and 200 inches a year. The river is about 70km long and...
  
  
• Hatton Oya
• Hulu Ganga
• Loggal Oya
• Uma Oya
• Badulu Oya
• Amban ganga