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.
The River Bourne at Winterbourne Gunner, a typical chalk stream
Commercial watercress production near New Alresford in Hampshire
Watercress or yellowcress is a species of aquatic flowering plant in the cabbage family, Brassicaceae.
Image: Watercress (2)
Image: Nasturtium officinale 00
Watercress beds in Warnford, Hampshire, England