Laja River is a river in Chile, along which can be found the Laja Falls. It is located in the Bio-Bio Region. The source of the river is Laguna del Laja in the Andes, then flows westward through the Chilean Central Valley and terminates into the Bio-Bio River, being an important tributary of it.
The Laja River is known among whitewater kayakers in Chile as Class 5 very steep and thrilling whitewater kayaking run. The Laja river actually forms from a drainage in the Lake Laja where the water exits at the bottom of the lake through the side of a mountain. Because the river is formed from exiting the bottom of the lake the river level is always constant.