River Derwent & Bassenthwaite Lake IPA

Location: North of the Lake District National Park, to the south of Cockermouth and north of Keswick. The A66 from Cockermouth runs alongside the lake.

Grid Reference: NY 226 262


River Derwent & Bassenthwaite Lake IPA has been recognised as one of 165 Important Plant Areas in the UK.

The key features of this IPA are:

  • One of the UK’s most important populations of Floating Water-plantain
  • One of the best UK examples of threatened habitats of:
    Nutrient poor acidic lakes on sandy plains
  • The River Derwent is one of the longest and most varied of the Lake District's rivers. It rises amidst the dramatic mountainous splendour of Borrowdale, flows through two very different lakes in Derwentwater and Bassenthwaite Lake, and then emerges onto the west Cumbrian plain and flows west to the Irish Sea at Workington.

    The source of the River Cocker is at the head of the Buttermere Valley. It flows north through Buttermere and Crummock Water to the town of Cockermouth where it joins the Derwent. The Derwent-Cocker is the largest oligotrophic, or nutrient poor, river in England that still retains high water quality and a natural channel. This low nutrient status is reflected in the abundance of bryophytes and the absence of a number of other plant species found in more nutrient rich rivers. There is, however, a natural succession of plant communities from source to mouth and the area is characterised by inland water bodies, bogs and marshes and broad-leaved deciduous woodland. It is ecologically important for its vascular plants.

    Plants you could see

    Derwentwater is the broadest and shallowest of the major Cumbrian lakes. The aquatic flora is that of a relatively low level, nutrient poor lake and typical species include water lobelia, intermediate water-starwort, alternate water milfoil, the uncommon awlwort and quillwort. Spiny-spored quillwort is also found here in one of its few English localities and the lake supports the nationally scarce floating water-plantain.

    The sheltered bays, where the water is locally more nutrient rich, support lesser pondweed and white and yellow waterlilies. Between Derwentwater and Bassenthwaite higher plant species become an important component of the river’s aquatic flora with intermediate water starwort, common water crowfoot and alternate water-milfoil co-dominating with the lichens and mosses. A number of other species also appear for the first time in the river including purple loosestrife.

    Bassenthwiate Lake is the fourth largest lake in the Lake District but one of the shallowest. It supports an extremely rich aquatic flora, including a wide variety of pondweeds, the nationally scarce floating water-plantain, six-stamened waterwort, a local northern species and the nationally rare thread rush and slender rush. Around Bowness Bay, vegetation grades into a range of wet grassland and fen communities. Sedges, rushes and tufted hair-grass are locally abundant and associated herb species include marsh-marigold, ragged robin, yellow iris, meadowsweet, greater burnet, common valerian, wild angelica and marsh cinquefoil.

    The extensive flood-plain fen at the south end of the lake is one of the best remaining examples in Britain and its meadows are dominated by reed canary-grass and tufted hair-grass with a rich tall herb flora including meadowsweet, common valerian, yellow loosestrife, yellow iris and wild angelica.

    The River Cocker differs from the main river in being smaller with a more stable flow regime. Above Buttermere the water is normally peat stained and aquatic mosses dominate the bryophyte rich flora of the river and banks. The nationally rare moss Schistidium agassizii is found on the Cocker. In Buttermere Dubs between Buttermere and Crummock Water the stable flows enable a rich and varied flora, including alternate water-milfoil, intermediate water-starwort, shore-weed and bulbous rush to develop on pebbles and gravel.

    Image: Bassenthwaite Lake © Bryn Davies under CC BY-NC-ND 2.0