The Hirakud Dam, one of the longest earthen dams in the world, is built on the river:

The Hirakud Dam is built across the Mahanadi river, about 15 km upstream of Sambalpur in Odisha.

Key facts:

The main dam is about 4.8 km long, and with the earthen dykes on both sides, the total length is about 25.8 km. It is one of the longest earthen dams in the world and is often described as the longest dam in India.

Its reservoir, the Hirakud Reservoir, is one of the largest artificial lakes in Asia, with an area of about 743 square km at full level.

The foundation stone was laid in 1946 by Sir Howthorne Lewis, Governor of Odisha, and Jawaharlal Nehru laid the first batch of concrete in 1948.

It was completed in 1953 and inaugurated by Nehru in 1957.

It was one of the first major multipurpose river valley projects after independence.

Purposes of the project:

• Flood control in the Mahanadi delta, which suffered frequent, devastating floods before the dam.
• Irrigation of large areas in the Sambalpur, Bargarh and other districts, making western Odisha a major rice-producing region.
• Hydroelectric power generation.

Wildlife:

• The Debrigarh Wildlife Sanctuary lies along the reservoir, and the reservoir attracts many migratory birds in winter.
• The Hirakud Reservoir was declared a Ramsar site in 2021.

About the Mahanadi:

• It rises near Sihawa in the Dhamtari district of Chhattisgarh.
• It flows through Chhattisgarh and Odisha and enters the Bay of Bengal near False Point, forming a large delta along with the Brahmani and Baitarani.
• Its length is about 851 km.
• It is the largest river of Odisha and is called the "Ganga of Odisha" in some traditions.
• Its major tributaries are covered in a separate question.
• The Mahanadi water dispute between Odisha and Chhattisgarh is under consideration by a tribunal set up in 2018.

Why not the other options?

• ✗The Brahmani and the Baitarani are other rivers of Odisha.
• ✗The Godavari flows mainly through Maharashtra, Telangana and Andhra Pradesh.