Hirakud dam is built across the Mahanadi River , about 15 kilometres from Sambalpur in Odisha. Hirakud Dam is one of the longest dams in the world about 26 km in length. There are two observation towers on the dam one is “Gandhi Minar” and another one is “Nehru Minar”. The Hirakud Reservoir is 55 km long used as multipurpose scheme intended for flood control, irrigation and power generation. It was one of the major multipurpose river valley project after Independence. The Hirakud Dam is a composite structure of earth, concrete and masonry. It is the longest major earthen dam in India, measuring 26 km including dykes, and stands across the river Mahanadi. The main dam has an overall length of 4.8 km spanning between two hills , the Lamdungri on the left and the Chandili Dunguri on the right. The dam is flanked by 21 km of earthen dykes on both the left and right sides, closing the low saddles beyond the adjoining hills. Hirakud Dam has three canals, namely Bargarh Main Canal, Sason Canal and Sambalpur Canal. Bargarh Main canal has a water discharge rate of 4000 cusecs.
Before the devastating floods of 1936, Sir M. Visveswararya proposed a detailed investigation for storage reservoirs in the Mahanadi basin to tackle the problem of floods in the Mahanadi delta. In 1945, under the chairmanship of Dr. B. R. Ambedkar, the Member of Labour, it was decided to invest in the potential benefits of controlling the Mahanadi for multi-purpose use. The Central Waterways, Irrigation and Navigation Commission took up the work. On 15 Mar 1946, Sir Hawthrone 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. 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 ₹1,000.2 million (equivalent to ₹70 billion or US$1.1 billion in 2016) in 1957. Power generation along with agricultural irrigation started in 1956, achieving full potential in 1966.
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 generators for an installed capacity of 259.5 MW. Power Station II is located 19 km southeast of the dam at Chipilima. It contains 3 x 24 MW generators. The entire installed capacity of the dam's power houses is 307.5 MW. Power House I and II were built in three stages. During stage I, four generators were installed at PH I and in stage II, the power channel two and Power House II was constructed. All three generators were installed at PH II along with two more at PH I by 1963. Between 1982 and 1990, the seventh and final generator was installed at PH I.
With successful irrigation provided by the dam, Sambalpur is called the rice bowl of Odisha. The project provides 1,556 km2 (384,000 acres) of kharif and 1,084 km2 (268,000 acres) of rabi irrigation in districts of Sambalpur, Bargarh, Bolangir, and Subarnpur. The water released by the power plant irrigates another 4,360 km2 (1.08×106 acres) of CCA in Mahanadi delta. The dam can generate up to 307.5 MW of electrical power through its two power plants at Burla, on the dam's right bank and Chiplima, 22 km downstream from the dam. In addition, the project provides flood protection to 9,500 km2 (2.3×106 acres) of delta area in district of Cuttack and Puri. Chiplima has gained prominence as the second hydroelectric project of the Hirakud Dam. A natural fall of 80 to 120 ft (24 to 37 m) in the river Mahanadi is used to generate electricity. The place is mostly inhabited by fishermen, whose deity Ghanteswari is very popular in the neighboring area. The state livestock breeding farm and agricultural farm are located here. The dam helps control floods in the Mahanadi delta and irrigates 75,000 km2 (19×106 acres) of land. Hydroelectricity is also generated. The Hirakud Dam regulates 83,400 km2 (20.6×106 acres) of Mahanadi's drainage.
There are remnants of temples submerged after the dam was completed in 1957. In the summer season, the receding water of the dam makes the structures become visible. The hidden treasures have finally caught the attention of historians, and steps are being taken to understand the historical significance of these temples, which periodically go under water, only to resurface again. Many temples have been destroyed after 58 years of underwater existence. However, some remain intact. Interest in these lost temples has been rekindled after two stones, etched with writing ('Shila Lekha'), were recovered from what is believed to be the Padmaseni temple of submerged Padmapur village. The temples located inside the reservoir area were part of the then Padmapur, one of the oldest and most populous in the region prior to the dam construction. More than 200 temples were submerged by the dam, nearly 150 temples have either perished or are underwater and about 50 are visible during summer. The lost temples present excellent opportunities for scuba diving enthusiasts to explore the underbelly of Hirakund Dam. The temples are visible to visitors on boat only during the summer months of May and June.
Cattle Island is located in one of the extreme points of Hirakud Reservoir, a natural wonder. It is one of the many islands within Hirakud Reservoir. Completely inhabited by wild cattle, without any trace of humans. It is near Kumarbandh village of Belpahar-Banharpali range which is about 90 km from Sambalpur. It can be reached by launch from Hirakund Dam. The island is a submerged hill, and before the construction of Hirakud Dam it was a developed village. During the resettlement period, villagers left some of their cattle behind; when the dam construction was over, the cattle settled on the hilltop. With the passage of time the nearby area filled up with the reservoir water, turning the hilltop into an island. Being away from mankind, the cattle are now wild, very swift and not easily caught. Living on a hilltop with dense forest, they are larger than tame cattle, almost all of which are white in colour. Nearby residents attempt to capture these animals from time to time, but these hunts are rarely successful. Though descended from tame cattle, these animals provide a contrasting picture of this breed of animal returning to life in the wild.
The dam with the channel provides an ideal environment for the wildlife. The Debrigarh wildlife sanctuary is located here. Several species of migratory birds visit the reservoir during winter. Nearly 20-25 species of birds are seen in the reservoir and common among them are common pochard, red-crested pochard, great crested grebe and several others.
Water from Hirakud Dam at a later stage was allocated to various industries, primarily for mineral processing and coal fired thermal power plants in Jharsuguda and Sambalpur districts.