The River Wylye is a chalk stream in the south of England, with clear water flowing over gravel. It is popular with anglers for fly fishing. A half-mile stretch of the river and three lakes in Warminster are a local nature reserve.

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.