Larger version of Thirlmere photo (PDF)

This is a photo of Thirlmere reservoir, a man-made lake created in the late Victorian era. In the mid 19th century Thirlmere valley bore no resemblance to its appearance today. Two small tarns, Leathes Water and Wythburn Water, sat in the bottom of the valley connected by a stream with a small causeway bridge running over it. At the south end there was a small hamlet with a pub.

However the Industrial Revolution in Manchester was creating a demand for more water in the suburbs and factories of the cities; this led to a search for good water sources. The search ended in Thirlmere and following an Act of Parliament, work was begun on both a dam at the north end, to stop the water flowing out of St Johns Beck to Keswick, and a 96 mile aqueduct to carry the water to Manchester. This was connected up for the first time in 1894.

Thirlmere is a glacial valley, with good water catchment fells either side and streams running down into the valley bottom. These features make Thirlmere one of the purest water sources in the country. Today this same aqueduct takes water to many other places on route to Manchester as well as being supplemented by water from Haweswater and many other smaller sources. 220 million litres of water per day flow through the Water Treatment Works sited 3 miles south of the reservoir.

United Utilities currently manage the reservoir and the surrounding 12,000 hectares of land. Their ranger has to look after the wildlife and protect the reservoir from pollution sources including day visitors, campers and farming chemicals. Non-powered craft are now allowed to use the reservoir but no swimming is permitted due to the danger of death by drowning in extremely cold, deep water.

200 lorry loads of timber are felled each year from the coniferous plantations surrounding Thirlmere; the rest of the woodland is deciduous and both woodland types contribute to the soil stability and therefore reduce soil erosion into the reservoir.

Thirlmere is filled up entirely by rainwater, the streams bringing it down into the lake. It seems bizarre that while there is so much freshwater around, many of the hill farms in the Lake District have no treated, clean water piped to them and rely on natural springs for their own water supply.

The Lake District has so many lakes, largely because of the volcanic rock which does not allow water to seep away. The high rainfall, combined with the extra deep glacial valleys, means that the valleys are able to store large volumes of water.

Grid reference of Thirlmere Dam: 309189 (English Lakes NE 1:25,000)

Important vocabulary:

rainfall, volcanic rock, water cycle, reservoir, flood, drought, mere (word of Viking origin meaning lake), aqueduct, pollution, erosion, coniferous, deciduous

Discussion starters/questions:

What would happen to the water levels in a drought?

How does water get into the reservoir?

Where does the rainwater come from, discuss the water cycle.

What use is it to plant trees around the reservoir?

Why is the water so pure?

Why are there no boats?

Why are there so many lakes in the Lake District?

Discuss possible pollution sources of the water

What causes ripples and why is the water so still?

Why is water pale blue/dark blue?

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