Lago Paimún is located in the Departamento Huiliches of Neuquén Province, within Lanín National Park, at an elevation of 875 meters above sea level. The lake covers approximately 16 square kilometers and stretches roughly 11 kilometers in length, forming the northern arm of Lago Huechulafquen, into which it drains. The two lakes are connected, making it possible to paddle between them. Lago Paimún is fed by glaciers originating on Volcán Lanín and by small streams that flow from the border with Chile.

The lake sits within a landscape of snow-capped mountains and dense forest. Volcán Lanín, the highest peak in the region at 3,740 meters, looms directly over the northern shore and is visible from virtually any point on the water. Wildlife in the surrounding area includes red deer, foxes, wild boar, hares, otters, and birds of prey. The Iglesia María Auxiliadora del Paimún, a chapel on the lakeshore, is a notable landmark along the shoreline.

A road runs along the north shore of the lake, providing access to the area. The Arroyo Germain campsite is situated on the lakeshore and offers views of both the lake and Volcán Lanín. The Hostería Paimún is also located nearby. From the western end of the lake, it is possible to walk along the south shore toward La Balsa and continue to Puerto Canoa on Lago Huechulafquen, suggesting a logical paddling corridor in that direction as well.

The lake has warm, transparent water. Because it lies within Lanín National Park, paddlers should consult current park regulations before launching, as the area falls within the Reserva de Biósfera Andina Norpatagónica. The nearest service towns are Junín de los Andes, approximately 103 kilometers away, and San Martín de los Andes. The lake has no towns directly on its shores. Fishing for rainbow and brown trout is a popular activity on the connected Huechulafquen system, which may mean sharing the water with anglers.