Which is the longest canal in India?

The Harike barrage stands in Punjab at the point where the Beas joins the Sutlej, and the Indira Gandhi Canal begins there as the Rajasthan Feeder before continuing as the main canal into Rajasthan.

The Upper Ganga Canal was opened in 1854 and is taken from the Ganga at Haridwar, from where it runs down the Ganga–Yamuna Doab and irrigates the districts of western Uttar Pradesh; the engineer associated with its construction is Proby Cautley.

The Grand Anicut, known in Tamil as Kallanai, was thrown across the Cauvery by the Chola king Karikala in about the second century to spread the river's water over the delta, and it still serves the canals of the Cauvery delta in Tamil Nadu.

The Buckingham Canal is a salt water navigation canal dug in the nineteenth century along the eastern coast, linking the lagoons and backwaters between Vijayawada in Andhra Pradesh and Chennai in Tamil Nadu, and it was used to carry goods and to relieve famine by moving grain.

Groundwater drawn through wells and tube wells irrigates the largest part of the net irrigated area of India, and its share has risen steadily since the Green Revolution because a tube well gives water on demand, close to the field and without waiting for a canal turn.