Cow Green Reservoir and the Tees

Cow Green was a sleepy backwater of Upper Teesdale, a remote farming and lead-mining community. Here the Tees, barely down from its birthplace on the windswept expanses of Cross Fell, meandered in a wide heather and marsh basin. There were two famous views: the first, the Teesdale Wheel, where the Tees flowed in a huge circle, and the second, Cauldron Snout, lay just beyond, where the river thundered down dolerite cliffs in one of Britain's most spectacular waterfalls.

It had long been known that the area was of great interest to botanists, and teams had often made pilgrimages here to see the unique collection of arctic alpine plants. In the 1950s and 60s there were rumours. Darlington needed more water and they had their eyes on Cow Green. Conservationists were up in arms. Letters were sent to The Times; scientists from all over the world protested that the site was just too valuable. Wainwright joined the protesters with the first edition of his little green Pennine Way Companion. He declared that to flood this land would be a desecration. A public enquiry was set up. Cow Green was chosen. Scientists and volunteers were allowed access to the site before flooding in order to remove specimens of the rare species and replant them above the proposed water line. By 1970 the dam had been built, the waters rose, slowly but surely, above the Teesdale Wheel until it was no more, and to the top of the concrete. Only Cauldron Snout survived.

What made Cow Green so special? It is believed to be the harsh climate and the presence of sugar limestone, a rock that has been baked by the intrusion of molten whin sill, the other predominant rock of the region. Behaving and looking like sand, its soils support a multitude of species, including spring gentian, dog violet, thyme, harebell, shrubby cinquefoil, primrose, and spring sandwort. The Teesdale violet only grows on Widdybank Fell, and tracts of juniper helped the survival of a large bird population.

The area is part of the Moor House-Upper Teesdale National Nature Reserve, which encompasses 18,285 acres (7,400ha) of the headwaters of the Tees. English Nature, who manage the reserve with the estate owners, have waymarked a nature trail that will form the latter part of this long walk. First though, the route heads east over Widdybank Fell to join the Tees downriver. It's a fascinating course, across the fields of lonely Widdybank Farm, through the meandering, ever tightening, valley of the Tees and between the jumbled rocks of Cronkley Fell and Falcon Clints. Each corner brings a new view, but each corner takes you further from civilisation, into a world of dark and dramatic heather hillscapes. The Tees is wide and shallow, and splashes over a bouldery bed. The path sometimes gets nearer to the river than you would like and you find yourself hopping over boulders smoothed by the boots of a thousand Pennine wayfarers.

Then you come to Cauldron Snout. Cow Green Reservoir hasn't stopped it foaming and it still thunders down those dolerite cliffs. An exciting path scrambles up by its side and comes to that dam and disappointment. Back in civilisation a hard stony track, then an even harder tarred road take you around the reservoir shores. If its spring your mood may lighten if you can just find the tiny blue blooms of the spring gentian.

Where to eat and drink

Try the Langdon Beck Hotel, which you pass on the way to the start of the walk. This welcoming free house country pub is child friendly and well-behaved dogs are allowed. The menu features traditional bar meals alongside dishes such as lamb Auvergne.

What to look for

On the south side of Slapestone Sike you'll notice a spoil heap and the concrete cap of a mineshaft. The remains are from a baryte (barium sulphate) mine, which operated until the 1950s. The mineral was used in the manufacture of paper and paint. Its high density also made it useful as a drilling mud (lubricant and coolant) for oil rigs. Near the beck you may also spot the white, star-like flowers of the toxin-loving spring sandwort.

While you're there

Take a look at that other waterfall, High Force, which can be reached on a short walk from a roadside lay-by north of the Bowlees Visitor Centre. Here the Tees falls in one drop 70ft (21m) into a deep pool in a gorge beneath dolerite cliffs.