Lago Huechulafquen is a glacial lake in Huiliches Department, Neuquén Province, within Lanín National Park in Patagonian Argentina. It stretches approximately 30 kilometers in length and up to 5 kilometers in width, covering a surface area of 78.2 square kilometers with an average depth of 142 meters. The lake sits in the Andean mountains roughly 25 kilometers from Junín de los Andes and 30 to 50 kilometers from San Martín de los Andes. Its primary outflow is the Río Chimehuín, a world-renowned fly-fishing river.

The main access point for water-based activities is Puerto Canoa, located on the lake's shore and the departure point for organized boat excursions. A road runs along the north shore, passing through several Mapuche communities, while another road touches the southern shoreline of Lago Epulaufquén. The lake connects to Lago Paimún to the west, and from virtually any point on the water the glaciated cone of Volcán Lanín dominates the northern skyline.

Because the lake lies entirely within Lanín National Park, paddlers should be aware that access to certain areas is restricted to protect the nature reserve. Organized catamaran excursions operate from Puerto Canoa, navigating through areas of the park that are otherwise difficult to reach. Boat rentals may be available through local operators, though it is advisable to confirm availability in advance with tour agencies in Junín de los Andes or San Martín de los Andes. Fishing on the lake and its outlet requires a valid Argentine fishing license; rainbow trout and brown trout are the primary species present, both introduced in the early 1900s.

Camping is available at sites along the lake, including Bahía Azul, which offers views of both the lake and the volcano. The lake is fed by glaciers and meltwater streams, meaning water temperatures remain cold year-round, consistent with high-Andean glacial lakes in Patagonia. Winds in Patagonia can be strong and unpredictable, a significant consideration for paddlers on a body of water this large and exposed. The surrounding landscape transitions from Patagonian steppe to Andean forest, and the lake's considerable depth and glacial origin contribute to notably clear water.