The Isthmus of Ofqui is a narrow isthmus that connects the Taitao Peninsula with the Chilean mainland. The isthmus is bounded in the south by the Gulf of Penas, in the north by the San Rafael Lagoon, in the west by the Taitao Peninsula and in the east by the Northern Patagonia Ice Field.

Much of the swampy isthmus is drained by San Tadeo River that flows in SSW direction to the Gulf of San Esteban.

Geologically it is considered the southern end of the Chilean Central Valley, and the Liquiñe-Ofqui Fault. The Isthmus of Ofqui lies close to the Chile Triple Junction where the Nazca Plate, the South American Plate, and the Antarctic Plate meet.

In 1937 the Chilean Government ordered the construction of a canal through the isthmus in order to open a direct passage from the Moraleda Channel to the Messier Channel and avoid going out into the open Pacific Ocean to get around the Taitao Peninsula:

1. a 2,200 m long, 17 m wide, 5 m depth Canal between the Laguna San Rafael and the Negro River to connect then the
2. Negro River (25 km).

The work began in 1937 under the management of the railways department of the Ministry of Public Works. Work continued until May 1943 when funds ran out.

• Laguna San Rafael National Park
• Liquiñe

• Martin Coombs (7 July 2009), A backdoor to the south, archived from the original on 6 June 2012, retrieved 8 April 2013
• J. Horacio Balmelli Urrutia, La apertura del Istmo de Ofqui: Un tema vigente, archived from the original on 5 November 2009, retrieved 8 April 2013
• Guillermo Arroyo Acuña (October 1944), El antiguo anhelo: El canal de Ofqui, Revista Cruz del Sur, archived from the original on 30 September 2011, retrieved 8 April 2013
• ¿Qué fue del Canal de Ofqui?, "En Viaje", October 1941, retrieved 8 April 2013

46°47′50″S 74°04′04″W / 46.79722°S 74.06778°W / -46.79722; -74.06778