Nahuel Huapi National Park is the oldest Argentine national park, in Patagonia in the foothills of the Andes mountains.
The park covers approximately 7050 km² and is located in the southwest of the Neuquén and northwest of the Río Negro provinces bordering with Chile. The largest city within the park and a base for tourism is the city of San Carlos de Bariloche. Villa La Angostura is another lakeside resort also within the boundaries of the park.
The park is famous for its rich wildlife and it covers many biotopes, due to altitudes ranging from 700 to 3,000 m and precipitation ranging from rain forests with 4,000 mm/yr on the western slopes to steppes with less than 300 mm/yr on the eastern side. The alerce or Patagonian cypress is a slow-growing conifer seen in the park. Other flora seen in the park include arrayanes, coihues, ferns, the caña colihue reeds, lengas, ñires, amancayes and arvejillas. The llao llao fungus is seen as beautiful irregular growths on the trees and is a symbol of the area and the name of the Hotel Llao Llao, a famous resort. Animals include river otters, huemuls, pudus, guanacos, maras, parakeets and condors.
There are many lakes in the park, including Lago Nahuel Huapi, Lago Mascardi, Lago Gutiérrez, Lago Traful, Lago Moreno, and Lago Guillelmo. The area is known as the Argentine Lake District.
Lake Nahuel Huapi contains several islands, including Isla Huemul, which hosted the Huemul Project, the Argentinian secret research project on nuclear fusion in 1949-1952.
The Quetrihué peninsula in the north of the lake has been set aside as a separate national park, Los Arrayanes National Park. Cerro Catedral is a 2,388m high peak within the Park and an important ski resort.
Cerro Tronador, on the Chilean border, is the highest mountain in the park at 3,491m. Bordering the National Park to the north is the Lanín National Park.