The River Wensum is a chalk river in Norfolk, England and a tributary of the River Yare, despite being the larger of the two rivers. The river is a biological Site of Special Scientific Interest and Special Area of Conservation.

Chalk streams are rivers that rise from springs in landscapes with chalk bedrock. Since chalk is permeable, water percolates easily through the ground to the water table and chalk streams therefore receive little surface runoff. As a result, the water in the streams contains little organic matter and sediment and is generally very clear.