The Río Ancoa is a tributary of the Achibueno located in Linares Province, Maule Region. The river is notable for its whitewater character, with the upper section offering a big-water feel at class 4, transitioning into class 5 rapids. The put-in is reached via a rough road, and the water at this point emerges from a tunnel on river right — an unusual feature worth noting when orienting at the launch.

The upper stretch above the second bridge is the most scenic portion, carrying significant volume with class 4 rapids before the gradient steepens. Approximately one-third of the way down, paddlers encounter a river-wide six-foot ledge hole that is a serious class 5 feature; the recommended line is to scout and portage on river right. After the second bridge, there is a sievey rapid that should be approached carefully, with the preferred route being a sneak on the left. From there, the river continues with class 5 whitewater to a dam, which requires a portage, followed by easier rapids down to the third bridge. The segment between the second and third bridges can be completed in under 30 minutes and avoids the more difficult portions of the shuttle road higher up.

Paddlers should be aware that a reservoir — the Embalse Ancoa — now inundates what was previously a runnable section of the river, leaving only the rapids below the dam intact for that lower stretch. The shuttle road in the upper section is described as rough and potentially problematic, making the bridge 2 to bridge 3 run a practical alternative for those wanting to avoid it.

For those seeking calmer water, there are cabin accommodations along the river near Linares that offer kayak access for flatwater paddling and swimming.