The Casiquiare river or canal (Spanish pronunciation: [kasiˈkjaɾe]) is a natural distributary of the upper Orinoco flowing southward into the Rio Negro, in Venezuela, South America.

In 1744 a Jesuit priest named Manuel Román, while ascending the Orinoco River in the region of La Esmeralda, met some Portuguese slave-traders from the settlements on the Rio Negro.

[7] During a 1924–25 expedition, Alexander H. Rice Jr. of Harvard University traveled up the Orinoco, traversed the Casiquiare canal, and descended the Rio Negro to the Amazon at Manaus.

[8] The origin of the Casiquiare, at the River Orinoco, is 14 kilometres (9 mi) below the mission of La Esmeralda at 3°8′18.5″N 65°52′42.5″W / 3.138472°N 65.878472°W / 3.138472; -65.878472, and about 123 metres (404 ft) above sea level.

Its mouth at the Rio Negro, an affluent of the Amazon River, is near the town of San Carlos and is 91 metres (299 ft) above sea level.

[9][10] In flood time, it is said to have a second connection with the Rio Negro by a branch, which it throws off to the westward, called the Itinivini, which leaves it at a point about 80 kilometres (50 mi) above its mouth.

[4] The Casiquiare is not a sluggish canal on a flat tableland, but a great, rapid river which, if its upper waters had not found contact with the Orinoco, perhaps by cutting back, would belong entirely to the Negro branch of the Amazon.

In the early 20th century, it was much used for the transit of large canoes, which were hauled across it from the Temi River and reached the Rio Negro by a little stream called the Pimichin.

The Casiquiare canal connects the upper Orinoco, 14 kilometres (9 mi) below the mission of Esmeraldas, with the Rio Negro affluent of the Amazon River near the town of San Carlos.