Lago Todos los Santos lies within the Vicente Pérez Rosales National Park in the Los Lagos Region of southern Chile, approximately 76 km east of Puerto Varas and 96 km northeast of Puerto Montt. The lake covers a surface area of 178.5 km², stretches 32 km in length and up to 16 km in width, and reaches a maximum depth of 337 m with an average depth of 190 m. It sits at an elevation of 189 m above sea level. A single island, Isla Margarita, lies within the lake. The waters are notably emerald-green in color, a characteristic attributed to their glacial origin, and the lake's surface acts as a reflective mirror for the surrounding forested slopes.

The lake is flanked by three prominent volcanoes — Osorno, Puntiagudo, and Tronador — and the catchment is largely covered with old-growth Valdivian temperate rain forests. The eastern shore is home to Villa Peulla, a small settlement that offers accommodation and ecotourism services. The lake's primary use by visitors is as a transit route for the Andean Lakes Crossing, a multi-lake journey connecting the Chilean Lake District to Bariloche, Argentina, meaning commercial boat traffic is a regular presence on the water.

Kayaking is a recognized activity on the lake, with calm coves available for paddling. However, the lake's large size, significant depth, and exposure to variable weather conditions in this part of Patagonia make preparation essential. Paddlers should carry warm and waterproof clothing, as the climate is highly changeable. As the lake falls entirely within Vicente Pérez Rosales National Park, leave-no-trace principles apply and visitors are expected to follow park ranger instructions and respect native fauna and flora.

Fishing is also practiced on the lake. Access to the western end is via Petrohué, which serves as the main gateway and is reachable from Puerto Varas. Despite the lake's scenic qualities and suitability for kayaking, independent paddling remains relatively uncommon compared to commercial boat tours, which run year-round. The park's protected status has preserved the surrounding old-growth forest and water quality, keeping the environment in good condition.