Information:  - The Kotmale River ( Sinhalese :   ) is the longest tributary of Mahaweli River . The river begins as the Agra Oya , in the Horton Plains . The Central Plains have an annual rainfall of between 125 and 200 inches a year . The river is approximately 70 km ( 43 mi ) long and drains a basin of about 58,534 ha ( 226 square miles ) . The river flows through a traditional area of ancient villages and tea plantations . King Dutugemunu spent his youth here . The Kotmale Oya flows into the Mahaweli shortly at Pallegama . Tributaries of the Kotmale Oya include the Nanu Oya , the Pundal Oya , the Puna Oya , and the Dambagastalawa Oya . The river was dammed between 1979 and 1985 as part of a hydro - electric project within the Accelerated Mahaweli Ganga scheme . The opening ceremony took place in August 1985 . Some 3,000 families had to be relocated top higher ground . The area has a history of geological instability .  - The Bay of Bengal, the largest bay in the world, forms the northeastern part of the Indian Ocean. Roughly triangular, it is bordered mostly by India and Sri Lanka to the west, Bangladesh to the north, and Myanmar (Burma) and the Andaman and Nicobar Islands (India) to the east.  - A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.  - Hydroelectricity is electricity produced from hydropower. In 2015 hydropower generated 16.6% of the world's total electricity and 70% of all renewable electricity, and was expected to increase about 3.1% each year for the next 25 years.  - The Mahaweli River (Mahawaluka nadee, literally "Great Sandy River"; ["mahawali gangai"]), is a long river, ranking as the longest river in Sri Lanka. Its drainage basin is the largest in the country, and covers almost one-fifth of the total area of the island. The real creation of Mahaweli ganga starts at Polwathura(at Mahawila area), a remote village of Nuwara-Eliya District in bank Nawalapitiya of Kandy District by further joining of Hatton oya and Kotmale oya.The river reaches the Bay of Bengal on the southwestern side of Trincomalee Bay. The bay includes the first of a number submarine canyons, making Trincomalee one of the finest deep-sea harbors in the world. The river and its tributaries are dammed at several locations to allow irrigation in the dry zone, with almost of land irrigated. Production of hydroelectricity 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.    What entity does 'kotmale oya' has the relation 'country' with?
sri lanka