Great Mountain Days in the Pennines. Terry Marsh

      The diversity of wildlife and plantlife is quite remarkable. Spring gentian grows here, the only place in England, while the country’s largest juniper woodland is here, too, in great abundance near High Force (see Walk 6), but also growing alongside the River Tees in a few places. An early morning visit is necessary to spot the black grouse, but at any other time there is a wealth of birdlife – skylark, lapwing, curlew, snipe, red grouse, redshank, common sandpiper, dipper, golden plover, pied and yellow wagtails, and ring ouzel – all of which tends to contribute to slow progress.

      The River Tees below Falcon Clints

      The ongoing track (surfaced) speeds on towards the dam of the reservoir.

      Cow Green Reservoir is 3km (2 miles) long and was built between 1967 and 1971 to supply the industries of Teesside. The reservoir acts as a river regulation reservoir, releasing water into the River Tees during dry conditions so that it can be abstracted further downstream.

      The reservoir, which rests against a backdrop of Dufton Fell and, further to the north-west, Cross Fell and the two Dun Fells, lies within the North Pennines AONB and European Geopark. The AONB was designated in 1988, and it became Britain’s first European Geopark in 2004.

      Walk down from the dam to the bridge spanning the Tees as it gushes from the base of the dam wall. Now, joining the southbound Pennine Way, take care descending the eastern side of the river for a fine view of Cauldron Snout, more a long cataract than a waterfall, and at 180m reckoned to be the longest waterfall in England. The awkwardness is short-lived, but care is needed while traversing slippery rocks until the level ground beside the river is reached.

      Once below the falls, at the confluence of the Tees and Maize Beck, turn eastwards below the impressive crags of Falcon Clints, the southern escarpment of Widdybank Fell. A clear path leads on, parallel with the river, the worst ground spanned by boardwalks, but with a few sections where care is needed traversing boulder downfall. Cronkley Scar on the other side of the river combines with Falcon Clints to create the narrow defile known as Holmwath.

      At the approach to Widdy Bank Farm, a gated stile gives into an enclosure, then go shortly left at another stile, beyond which a grassy path runs on above the river. As the river swings to the south-east, the path bears away across rough pasture and a few walled fields before heading down to Sayer Hill Farm.

      Here, turn right, using the farm access to walk to Saur Hill Bridge, which spans Harwood Beck. On reaching the bridge, turn left before it, leaving the Pennine Way and taking to a path alongside the beck, and follow this beckside path to a crossing point on the road from Langdon Beck. Now, turn left, and simply follow the gently rising road across undulating pastures for 4km (2½ miles) back to the car park overlooking Cow Green. There is an air of openness about this return section, enlivened throughout by bird song and, in spring especially, a wealth of wild flowers, both of which combine to speed the return journey.

      The River Tees below Cronkley Scar

WALK SIX

      High Force and Cronkley Fell

Start point	Bowlees NY908283
Distance	20.5km (12¾ miles)
Height gain	372m (1220ft)
Grade	demanding
Time	6hrs
Maps	Ordnance Survey OL31 (North Pennines: Teesdale and Weardale)
Getting there	Bowlees picnic area car park
After-walk refreshment	Pubs, cafés and restaurants in Middleton-in-Teesdale

      For much of its long journey the Pennine Way is charted across desolate acres, the preserve of experienced walkers. But for a while, as it progresses northwards from Middleton-in-Teesdale, it relaxes its challenge and injects a soft, pastoral interlude of riverside meadows before heading for the highest ground of all on Cross Fell. In this gentler stretch, the River Tees holds sway, just a few miles from its source. In places it meanders smoothly over a wide bed of rock; elsewhere it cascades forcefully with all the might of a major river over rocky downfalls.

      The Route

      Once a remote corner of the North Riding of Yorkshire and part of the ancient Forest of Teesdale in which deer roamed freely, the area that the walk passes through now lies entirely within the county of Durham. Middleton-in-Teesdale is the largest town hereabouts, formerly a local centre of lead-mining activities.

      From a long trail of boulders, it is possible to chart the course of the glacier that fashioned this region more than 10,000 years ago. It swept over gaps from the Eden valley, the Lake District and even the south of Scotland, carrying Shap granite and Borrowdale lava as far as the mouth of the Tees, where an accumulation of granite pinpoints what must have been the terminal moraine of the Tees glacier.

      The walk begins from a parking and picnic area at Bowlees. From here take a nearby footbridge and walk through Bowlees to the main road. There, opposite the telephone box, take to a clear path towards woodland flanking the unseen River Tees. Once in the woodland, a clear path leads down to cross the river by Wynch Suspension Bridge. The original Wynch Bridge was built in 1704 for miners, but it collapsed in 1820 and had to be rebuilt 10 years later.

      Immediately, the Tees puts on a show in the form of Low Force, a place where the riverbed is wide and punctuated by islands of dolerite. Set against a backdrop of dark woodlands, this is the Tees at its most beautiful.

      Climb the steps beyond the bridge and set off beside the Tees. This is a delightful stretch of the Pennine Way, which, at the right time of year, produces a display of plants that has given Teesdale an international reputation among botanists. Globe flower seems to grow everywhere, while among the rocks shrubby and alpine cinquefoil have found root. The most famous of Teesdale’s plants is the spring gentian, making its home here among other rarities, the alpine forget-me-not, bitter milkwort, bog sandwort, bird’s-eye primrose and others.

      Why such great plant diversity should appear here seems a puzzle – but the answer lies in the study of geology and early land formations. Teesdale (and parts of Scotland) were grassy islands in a vast forest, fragments of the carpet of tundra that covered Britain after the Ice Age. Later, when the climate improved, these areas were shaded out by trees. Carbon dating of pollen remains in the underlying peat reveals a history going back to the last Ice Age.

      Further on, juniper bushes cloak the slopes of Keedholm Scar. Juniper wood was once gathered to make high-quality charcoal, and the berries to flavour London gin.

      Looking along the Pennine Way to Cronkley Fell

      The river bends sharply just past Keedholm Scar, and suddenly the air is filled with a distant rumbling, the sound of the most famous of Pennine waterfalls, High Force. A slight diversion at metal railings is necessary to get a decent view from this side of the river, but care is needed this close to the edge. The Force is a dramatic plunge over a shelf of dolerite and shale of some 21 metres (70ft), dark brown and peaty, often lost in a fine mist of spray. This is not the highest waterfall in the country by any means, but it is the biggest, and a sight everyone should see.

      Upstream, the sound of the falls soon dies away and the Tees resumes a more docile air, rising in restless moorland wandering to its source high on the southern flanks of Cross Fell. The double falls of Bleabeck Force are nothing by comparison, a mere ripple. Ahead the route follows the Pennine Way as it climbs onto the shoulder of Bracken Rigg to an old Pennine Way marker post. From here it descends to a step-stile near a wall