Estero Nilahue is a coastal stream in the O'Higgins Region of Chile that originates in the Cordillera de la Costa and flows into the Pacific Ocean via Laguna Cáhuil. Its drainage basin covers 1,776 km². The waterway forms from the confluence of Estero Los Coipos — itself fed by Esteros Altos de Caune and El Parrón — and receives additional tributaries including Estero Quiahue (27 km), Estero Lolol (23 km), and Estero Pumanque (21 km) from the east. The estero empties into the southeastern end of Laguna Cáhuil, through which it reaches the ocean.

Kayak tours of the estero operate out of the Pichilemu area, with at least one outfitter running guided trips that include transport from Pichilemu to the southern end of Cáhuil. These excursions typically last three to four hours. The paddling character is calm enough to be suitable for participants of a wide range of ages and experience levels, making it accessible to recreational paddlers rather than only those seeking technical whitewater.

The estero passes through a landscape that retains scattered remnants of native forest along its banks. The area around Cáhuil is historically significant for salt production — marine salt deposits at the mouth of the estero have long supported the local economy, and the ruins of former salt works (salinas) are visible along the route. Autumn paddling on the estero has been documented, suggesting the waterway is navigable across multiple seasons.

Wildlife viewing is a notable feature of the experience. Species observed in the corridor include Coscoroba Swans, Black-necked Swans, Taguas (coots), various duck species, and herons. The combination of birdlife, remnant native vegetation, and the historical salt-working infrastructure gives the estero a distinctive character that blends natural and cultural interest within a relatively short paddle.