Lago Errázuriz / Lago Roca is a glacial lake situated in the southern portion of Isla Grande de Tierra del Fuego, straddling the border between Argentina and Chile. The Argentine portion lies within Tierra del Fuego National Park, while the Chilean side falls within Yendegaia National Park. The lake runs roughly northwest to southeast between the Guanaco and Pirámides mountain ranges of the Andes, stretching approximately 11 kilometers in length with an average width of about 1.5 kilometers. Two-thirds of the lake's extent lies in Chilean territory. The lake was formed by the natural damming of the Río Lapataia by a glacial moraine, and the Río Lapataia serves as both an inflow and the primary outflow. Additional tributaries include the Río Rojas and the arroyo Guanaco.

The lake carries three names reflecting its layered history: Lago Roca on the Argentine side, named for President Julio Argentino Roca; Lago Errázuriz on the Chilean side, named for President Federico Errázuriz Echaurren; and the indigenous name Acigami. The dual presidential naming commemorates the "Abrazo del Estrecho" of February 15, 1899, when the two presidents met aboard the cruiser O'Higgins to resolve a territorial dispute. In Argentina, the lake was officially known as Lago Acigami from 2008 until 2024, when the government restored the name Lago Roca.

The lake is a recognized tourist destination, accessible by land from within Tierra del Fuego National Park, with the Argentine shoreline reachable by road. Visitors have also arrived by boat as part of organized excursions. The lake supports populations of rainbow trout and brook trout, making it a destination for fly fishing. The lake features weed beds and shallow areas with emergent vegetation at the lower end, as well as open water suitable for drifting in a small boat. The surrounding landscape is defined by Andean mountain ridges and the broader subantarctic environment of Tierra del Fuego.