Hirakud Dam is built across the Mahanadi River, about from Sambalpur in the state of Odisha in India. It is the longest earthen dam in the world. Behind the dam extends a lake, Hirakud Reservoir, long. It is one of the first major multipurpose river valley projects started after India's independence. Hirakud Reservoir was declared a Ramsar site on 12 October 2021. Construction history On 15 March 1946, Sir Hawthorne Lewis, the Governor of Odisha, laid the foundation stone of the Hirakud Dam. A project report was submitted to the government in June 1947. Pandit Jawaharlal Nehru laid the first batch of concrete on 12 April 1948. In 1952, Mazumdar Committee was appointed by the government to oversee the soundness and technical feasibility of the project. The committee has envisaged costs of 92.80 crore for the project and that the construction of the main dam would be complete by June 1955. It also said that by 1954–55 a total of would be irrigated and that 48,000 kW of electric power would be generated. However, the dam was completed in 1953 and was formally inaugurated by Prime Minister Jawaharlal Nehru on 13 January 1957. The total cost of the project was in 1957. Power generation along with agricultural irrigation started in 1956, achieving full potential in 1966. Technical details Structure The Hirakud Dam is a man-made structure of earth, concrete and masonry. north of Sambalpur, it is the longest major earthen dam in the world, measuring including dykes, and stands across the river Mahanadi. The main dam has an overall length of spanning between two hills; the Laxmidungri on the left and the Chandili Dunguri on the right. The dam is flanked by of earthen dykes on both the left and right sides, closing the low saddles beyond the adjoining hills. The dam and dykes together measure . It also forms the biggest artificial lake in India, with a reservoir holding at full capacity, with a shoreline of over . There are two observation towers on the dam one at each side. One is "Gandhi Minar" and the other one is"Jawahar Minar". Both the observation towers present extensive views of the lake. Power houses The dam supports two different hydroelectric power houses. Power House I is located at the base (toe) of the main dam section and contains 3 x 37.5 MW Kaplan turbine and 2 x 24 MW Francis turbine