Lago Pirihueico is a glacially formed lake situated in the Panguipulli Commune of the Los Ríos Region, at a surface elevation of approximately 586 meters above sea level. The lake occupies a geological fault line shared with Lago Panguipulli to the west and Lago Lácar across the Argentine border to the east. Its elongated shape — roughly 23 kilometers long and 2 kilometers wide — makes it well suited as a waterway, and it has historically served as a transit corridor between Chile and Argentina via the Paso Hua Hum. Maximum depth reaches 145 meters, with an average depth of around 62 meters. The lake's waters are described as blue-green in appearance, bordered by native Valdivian rainforest that includes species such as Nothofagus dombeyi, Podocarpus nubigenus, Embothrium coccineum, and ulmo. The southern shore falls within the Huilo Huilo Biological Reserve.

The primary access point for paddlers is Puerto Fuy, a small village on the western end of the lake. A ferry service — the Barcaza Hua-Hum — operates between Puerto Fuy and Puerto Pirihueico at the eastern end, which can be useful for one-way crossings or logistics. The lake drains westward via the Río Fuy, which flows toward Lago Panguipulli and offers whitewater paddling ranging from Class II to Class V in its various sections; the Lower Fuy is rated Class II/III and is considered appropriate for beginners and intermediates.

Kayaking is explicitly listed among the recreational activities available on the lake. The surrounding landscape includes views of the Mocho-Choshuenco volcano and Andean peaks, with trails and viewpoints accessible from Puerto Fuy. Wildlife observation and sport fishing (requiring a SERNAPESCA license) are also practiced in the area. The southern shoreline's inclusion in the Huilo Huilo Biological Reserve may carry specific access or conduct regulations, and paddlers should verify any applicable rules before entering that zone.

The lake's glacial origin means water temperatures are likely cold year-round, though specific temperatures by month or season are not documented. The area around Puerto Fuy has a small population of roughly 1,000 people in the broader Choshuenco area, with basic amenities available. Guided fishing and paddling services operate out of Puerto Fuy, including full-day excursions with equipment and lunch provided.