The Incomappleux River is a major tributary of the Columbia River in British Columbia, Canada, entering that river via the Beaton Arm of Upper Arrow Lake. The area is the upper end of the Lardeau district. The river's course is nearly due south from its origin in the Selkirk Mountains at the southwest toe of the Illecillewaet Neve, which is on the south side of the Rogers Pass and is also the source of the Illecillewaet River.