The Groot River (English: "Large River") of Western Cape Province is a South African river. It should is not to be confused with the Groot River of Eastern Cape and the Groot River of Southern Cape provinces.
It is formed by a number of small tributaries including the Twee River and Lang River, flows off the eastern slopes of the Cederberg Mountains, south-east of Citrusdal. The river flows in an easterly direction through the Skurweberge Mountains where it joins the Riet River that rises as the Winkelhaak River and Houdenbeks River north of Ceres. Below this confluence, the Groot River is joined by the Brandkraals River and Matjies River, after which it flows into the Doring River.
The Clanwilliam Yellowfish (Labeobarbus capensis), a local endemic classified as Vulnerable by the IUCN, is still found in this river.