The Río Maullín originates as the outflow of Lago Llanquihue in the city of Llanquihue and flows generally southwestward for approximately 85 kilometers before emptying into the Gulf of Coronados via a tidal estuary. The river drains a basin of roughly 3,972 square kilometers and carries an average discharge of around 100 cubic meters per second. The lower course transitions into a tidal estuary, which is an important consideration for timing paddling trips in that section.

The 1960 Valdivia earthquake triggered landslides that altered the river's navigability, and today the Río Maullín can only be traveled by small boats and human-powered craft. This has effectively preserved the river's natural surroundings, keeping its flora and fauna largely intact. Paddlers moving through the corridor encounter dense riparian forest, networks of wetlands, and narrow channels. One particularly notable feature is a submerged forest — a section where trees stand partially inundated, creating a distinctive paddling environment that draws considerable visitor interest. The wetlands along the river, especially in the estuary near Laguna Quenuir, support exceptional diversity of aquatic birdlife compared to other stretches of the Chilean coast.

A well-documented multi-day route runs the full length of the river over three days and two nights, putting in near the source at Lago Llanquihue and finishing at Pangal beach near the city of Maullín. The itinerary passes through the rural sectors of El Gato, Puelpun, Olmopulli, Cebadal, Peñol, and the wetlands of the Cariquilda River. Overnight accommodation in rural houses and glamping on the riverbank is available along this route. Shorter half-day and full-day kayak and SUP tours also operate out of Llanquihue, with a meeting point at kilometer 2.4 on route V-155 on the coastal road. These shorter trips typically include 2.5 hours of paddling with stops for birdwatching.

Insect repellent is advisable near the river, as horse flies have been noted in the area. Light-colored clothing is also recommended to reduce attraction to biting insects. The river supports populations of brown trout, rainbow trout, and salmon, making it a destination for fishing as well as paddling.