The importance of the Thames Region?

Thames Water LogoHLF useWhy is the Thames Water region so important for freshwater biodiversity?

Water-violet_copyright Evan Jones

Water Violet – Evan Jones

Despite the pollution and destruction of freshwater habitats, the Thames Valley still has many wildlife rich, beautiful and varied freshwaters. One important reason for this is that, even though the main river network is quite polluted and damaged, the river and its floodplain, the many tributary streams, the ponds, the lakes, the floodplain marshes and wet meadows, are all part of an ancient wetland landscape which, despite the last 5000 years of human activity, still provide home for a great variety of freshwater plants and animals. Despite all the pressures, the Thames catchment still has three of England’s 20 top freshwater biodiversity hotspots: the Oxford area, the Thames Basin (particularly the heaths and floodplains west of London) and the Thames Estuary.

The lower-lying parts of the Thames valley has been a wetland since the last Ice Age, and even though from Neolithic times 5000 years ago we have been reducing, polluting and fragmenting those freshwater habitats, a network of still and flowing waters still survives. We have also added new freshwaters by making ponds, digging for gravel (leaving behind the many lakes that now pepper the region) and even creating new stretches of river, like the New Cut at Windsor which shortens the route for boats on the Thames or the Jubilee River which helps reduce flooding in Maidenhead.

Although at first sight it might seem that the Thames Valley of 8000 years ago, with its beavers, aurochs and wolves, has little to do with the modern world, the less conspicuous water plants animals show us the true continuity of the story. Although the wolves and aurochs are no longer part of the landscape, the smaller, less conspicuous, water beetles, freshwater snails and water plants that make up that environment are still here, often hanging on in little pockets of clean water. For example, archaeological investigations at Runnymede found the delicate shells of the pollution sensitive Glutinous Snail in 5000 year old Neolithic riverside deposits. Fast forward 5000 year to the 19th century, and the species could still be found from Battersea to at least Oxford. But by the middle of the 20th century this creature – a living link like many other wetland plants and animals to pre-history – was in decline. As pollution worsened so did the plight of the Glutinous Snail, and it finally became extinct in the Thames Valley (and in the whole of England) in the early 21st century[1], almost certainly as a result of water pollution. It has undergone a similar decline over much of its range in Western Europe.

Glutinous Snail

Figure 1. A Glutinous Snail from Llyn Tegid (Powys), the last known site in the United Kingdom. Once found all down the Thames Valley, from Oxford to London and in other parts of the Thames catchment (as well as other parts of England), this creature is now essentially lost from the landscape. This photograph shows an animal that is part of a ‘rescue’ captive breeding population from Llyn Tegid, maintained by Ian Hughes. Photo: Ian Hughes

Pollution sensitive water plants have gone much the same way as the sensitive Glutinous Snail. Detectable in the pre-history in the sediments of river floodplains, which are often exposed when gravel is excavated, they tell story of 10,000 years of continuity, disrupted particularly over the last 200 years. Around Oxford, for example, in the 17th century ‘every little ditch’ supported the pollution intolerant Water-violet. Now, the ditches are still there but the plant isn’t as it has been banished to a few remaining clean water ponds and pools on the floodplain, and to its principle stronghold in Otmoor north-east of Oxford.

Despite the stresses on freshwaters the Thames catchment still has a wonderful variety of beautiful, charismatic and endangered freshwater plants and animals, although many are hanging on by the skin of their teeth. These survivors against the odds – which contribute so much to the beauty and diversity of freshwater ecosystems, are found in all kinds of waterbodies, although the largest number are (perhaps contrary to what is commonly believed) found dependent on ponds and small lakes, rather than in rivers.


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[1]Whitfield M, Carlsson R, Biggs J, Walker D, Corfield A, Fox G, Williams P, 1998. The ecology and conservation of the glutinous snail Myxas glutinosa (Müller) in Great Britain: a review. J. Conchol. 2:209-221.