The importance of chalk streams

Chalk stream at Winnall Moors © Martin de Retuerto

For World Action on Rivers Day we celebrate and explore our chalk streams, some of Hampshire's most special habitats.

When we think of globally rare habitats, we often picture rainforests or the arctic tundra. But here in Hampshire we’re lucky to have something found almost nowhere else on earth: a number of beautiful chalk streams. Winding from the county’s northern reaches and into its heartland, these hidden gems quietly bring an abundance of life to the landscape.

Unlike the iconic Rivers Test and Itchen, which they feed, these streams aren’t as showy. Some flow only occasionally, transforming into grassy hollows for weeks or even months at a time. Yet whether wet or dry, these spaces have immense value for wildlife – they are home to an incredible range of species, many of which are ideally suited to their changeable nature.

The key to the streams’ unique qualities lies within the landscape itself. Much of Hampshire’s bedrock is chalk. Its structure is riddled with tiny holes, making it an excellent water-storing aquifer. When the rock can hold no more, the water bursts free in the form of springs; this is the source of our chalk streams.

But the aquifer is more than just a storage area. Water emerges from it filtered and mineral-rich, with a relatively cool temperature and constant flow in all seasons. The resulting mixture of dense vegetation and clean gravel is attractive to wildlife; a healthy chalk stream can house brown trout, water voles, kingfishers, damselflies, white-clawed crayfish, and more.

Unfortunately, this amazing geology does have a downside: water can take decades to travel through the aquifer, giving the landscape a long memory for pollutants. Above ground, stream modification and mismanagement add additional pressures like sedimentation and the overgrowth of algae. Much of the resident wildlife is specialised and unable to thrive elsewhere.

These issues pose a real threat to the health of our chalk streams and the wider landscapes through which they flow. There are also implications for the Test and Itchen, and even the marine environment beyond, which inherit any problems that travel downstream. The streams are precious in themselves, but also the start of a journey in which every step matters.

The Trust is currently very active on the headwaters through the Watercress and Winterbournes Landscape Partnership Scheme. As a partner, we’ve joined forces with local communities and 15 other organisations to protect, enhance, and celebrate these streams. Our actions range from habitat improvements and heritage restoration to community grants and creative activities.

Find out more