The world's longest man-made waterway (canal) is the:

The Grand Canal (Beijing-Hangzhou Grand Canal) of China is the longest artificial waterway (canal) in the world, at about 1,794 km (with all its sections, the canal system is often given as more than 2,500 km).

About the Grand Canal:

• It runs from Beijing in the north to Hangzhou in Zhejiang province in the south.
• It connects five major rivers: the Hai, the Yellow (Huang He), the Huai, the Yangtze and the Qiantang.
• It passes through the provinces of Hebei, Shandong, Jiangsu and Zhejiang, and the cities of Beijing and Tianjin.
• Its earliest sections date back to the 5th century BCE.
• It was greatly extended and linked into a single system during the Sui dynasty (581-618 CE), under Emperor Yang.
• It was rebuilt and straightened during the Yuan dynasty (13th century), which made it run directly to Beijing.
• It was used mainly to transport grain from the fertile south to the capital and armies in the north, and helped unify China economically.
• It is the oldest and longest canal in the world still in use; parts are still used for shipping.
• It was inscribed as a UNESCO World Heritage Site in 2014.
• It is now part of the "South-North Water Transfer Project", which carries water from the south to dry northern China.

Other famous canals:

• Suez Canal (Egypt): about 193 km; connects the Mediterranean Sea and the Red Sea; opened in 1869; designed by Ferdinand de Lesseps; nationalised by Egypt in 1956.
• Panama Canal (Panama): about 82 km; connects the Atlantic and Pacific Oceans; opened in 1914; handed to Panama in 1999; uses locks; expanded in 2016.
• Kiel Canal (Germany): connects the North Sea and the Baltic Sea; one of the busiest artificial waterways.
• Erie Canal (USA): connects the Hudson River and the Great Lakes; opened in 1825.

Canals in India:

• Indira Gandhi Canal (Rajasthan Canal): the longest canal in India; begins at the Harike Barrage (Punjab), at the meeting of the Sutlej and Beas rivers, and irrigates the Thar Desert.
• Buckingham Canal: a navigation canal along the Coromandel Coast (Andhra Pradesh and Tamil Nadu).
• National Waterway 1 (Ganga) is India's longest national waterway.

Why not the other options?

• ✗The Suez Canal is much shorter (about 193 km).
• ✗The Panama Canal is about 82 km long.
• ✗The Indira Gandhi Canal is the longest canal in India, but shorter than the Grand Canal.