The Río Diguillín is a low-volume whitewater river in Chile's Ñuble Region, draining from the peaks of Reserva Nacional Nuble near the Argentine border and flowing roughly 100 kilometers before joining the Río Itata near the locality of Liucura Bajo. The upper section originates in the Valle de Aguas Calientes area at the base of the Chillán Volcano (3,212 meters), and the river is characterized by a granite streambed, crystal-clear water, and pool-drop rapids that make it a technically interesting run.

The typical paddled section runs approximately 6 kilometers. Access involves leaving a shuttle vehicle at the takeout and driving upstream to the put-in. A locked gate may be encountered on the approach road; paddlers can gain entry by stating they are visiting Reserva Nacional Nuble, for which a 2,000 peso entrance fee applies. The run is best suited to the winter and spring months, with early spring — September through early October — considered the prime window. At that time of year, the river carries sufficient flow from snowmelt off the surrounding peaks.

The river flows through a canyon setting with granite walls and clear water. Just below the community of Los Lleuques, the waterfall of Estero Renegado enters the river and is a notable feature along the route. The surrounding area includes Reserva Nacional Nuble and Santuario Los Huemeles de Niblinto, both protected natural areas. The nearby town of Las Trancas offers lodging and dining, and the Termas de Chillán hot springs are accessible in the area, making it possible to combine a paddling day with other activities.

Other rivers in the broader region include the Longaví, Achibueno, and Laja, which may be of interest to paddlers planning a multi-river trip. The Diguillín's flora and fauna are noted as distinctive, and the river corridor functions as a biological corridor. There are ongoing conservation concerns related to proposed dam projects — specifically the Embalse Zapallar and Punilla — which local communities and environmental groups have opposed, though these have not yet altered the river's current free-flowing character.