Mike Dilger’s wildlife watching

In his series of great places to watch wildlife in the UK, the star of BBC One’s The One Show this month turns our attention to crystal-clear waters that create a habitat that’s almost exclusive to Britain.

Why we should treasure our remarkable chalk streams

Characterised by gin-clear waters, flowing over gravelly bottoms through emerald-green beds of aquatic plants, chalk streams are a quintessential habitat of the pastoral English lowlands. Large parts of the UK don’t have these very special waterways, and that’s down to geology.

These alkaline streams and rivers are not just world-renowned for their fly-fishing, but also celebrated in culture. The writer Isaac Walton, for example, who is considered the father of angling, took inspiration from his fishing trips along chalk streams when penning The Compleat Angler, first published in 1653. Artist John Constable famously captured the beauty of the Hampshire Avon in his 1831 painting of Salisbury Cathedral, now on display at Tate Britain. More recently, a 2014 report by WWF identified a total of 224 English chalk streams or rivers, all located along the band of chalk that sweeps diagonally across the east and south of the country. If you think that sounds like a decent count, astonishingly it’s 85 per cent of the global total. With the remaining 15 per cent in northern France, it wouldn’t be hyperbole to say chalk streams like ours don’t exist anywhere else in the world.

All chalk streams emanate from underground aquifers. The water that bubbles out of the springs has been converted from rainwater falling on chalky hills to chalk-water by the transformative process of percolation. As it becomes purified and fortified with minerals on its journey through the chalky bedrock, the crystal-clear product that resurfaces tends to be cool, with a temperature of about 10°C. Being relatively cold, the water can hold higher concentrations of life-giving, wildlife-enhancing oxygen, all the way from source to mouth.

Moreover, the flow remains reasonably constant, irrespective of season. This steady flow of cold, clear water coursing through meandering, gravelly channels creates a rich ecosystem. The writer Charles Rangeley-Wilson likens chalk streams to a “watery Garden of

Eden”. Streams in good condition may have beds of up to five species of closely related water crowfoot swaying in the current, together with luxurious, green bearded assemblages of water starwort, watercress and water parsnip.

Pure delight

The combination of lush aquatic vegetation and excellent water quality is perfect for mayflies, caddisflies and stoneflies, whose eggs, larvae and adults in turn sustain a variety of fish – from bullheads to grayling, brown trout and brook lamprey. The fen-like bankside vegetation that flourishes on any uncanalised stretches also supports resurgent populations of water voles and otters.

But as southern and eastern England is the most populated and most intensively farmed part of our landscape, it’s perhaps unsurprising that chalk streams and rivers reflect a long history of human intervention. Chalk watercourses have provided water for drinking, farming and industry for centuries. Today, their aquifers supply 70 per cent of the south-east’s public drinking water.

In addition to increasingly unsustainable water abstraction practices over the last 100 years, effluent discharge and physical modification for land drainage and flood defence have also contributed to a significant decline in water quality. The recent WWF report, for instance, revealed the sobering statistic that just a quarter of all streams were in good ecological health.

With expensive real estate and prime angling spots dominating many chalky watercourses, naturalists must be prepared to be denied access to some of the best stretches. But with the cities of Winchester, Salisbury and Norwich, to pick but three examples, all positioned along chalk streams and rivers, you can still access some lovely riverine walks.

A WWF report revealed the sobering statistic that just a quarter of all streams were in good ecological health.

Clockwise from top left: the River Avon in Dorset, where watercress lines the banks; water voles can be spotted amid the vegetation; the delicate white blooms of water crowfoot grace streams in spring and summer; grayling are found in fast flowing rivers; the clear water of the River Itchen; there’s no mistaking a kingfisher.

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