The River Thames is London’s most special natural resource that can be enjoyed by all the family on a healthy walk along the parks, towpaths and open spaces that line the riverbanks. Below is a brief introduction to the fascinating habitats and wildlife found along the River Thames including the main species that can be seen and information on how different habitats are managed. The influence of the tide, human activity, invasive species, the biodiversity action plans and climate change are explored.
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The Natural River
In its natural state the River Thames would have been very different – a shallow, meandering stream flowing through a wide bed of river gravels below the mass of Richmond Hill. Following summer storms and winter rains this would easily flood. Torrents of water would fill the river, spilling across an extensive floodplain of marsh, reedbed and swamp extending inland for many miles. It is believed that a series of ‘falls’ or rapids were present at Teddington, Glover’s Ait and Isleworth.
As human habitation spread, the Thames was slowly changed. Wetlands were drained and the river corridor was ‘canalised’ or narrowed to allow navigation to take place. This caused the tide to extend much further upstream than was natural. Agriculture thrived on the rich soils and more recently large areas of the floodplain were built on. As the river changed wildlife slowly adapted to these artificial environments finding new niches to thrive in. Today, although almost entirely man-made the river corridor provides some of the best environments in London for a wide diversity of wildlife to flourish.
The Tides and the Floodplain
Upstream of Teddington the river is freshwater. Between Teddington and Richmond Lock the river is tidal but water levels are artificially maintained (at low tide) to a depth of at least 1.5m for navigation. It is only below Isleworth that the full extent of the tide is experienced. At 7m the Thames has one of the highest tidal ranges in the world. Along large lengths of the Arcadian Thames the flood defence line is located quite some way inland. As climate changes and sea levels rise it is expected that these areas will flood more regularly necessitating changes to the management of established wildlife sites through the restoration of lost floodplain habitats such as wet meadows, reedbeds and tidal creeks.
The River Thames is a wildlife super highway – a linear corridor that allows wildlife to move between different open spaces through the very centre of the capital. The river is managed to allow a mosaic of different habitats to thrive including (moving from the river inland across the floodplain): the water itself, the foreshore, the riverbank, the tree line, wet woodland, ponds, grazed wet meadows, hedgerows, scrub, woodland and open parkland. Priorities for managing wildlife habitats are set out in the Biodiversity Action Plans (see links at bottom of the page) and the TLS Towpath Management Plan .
Just 60 years ago the River Thames was biologically dead. Since then it has been cleaned up and is now one of the cleanest metropolitan estuaries in the world, supporting over 120 different species of fish including eel, carp, perch and sea lamprey.
The gravel beds of the upper tideway are an important nursery ground for several species of North Sea fish notably flounder. Above the water insects flourish including: dragonflies, mayflies, caddis flies, mosquitoes and midges – the latter providing an ideal food source for all manner of bats. Some of the rarest riverside creatures are found on the islands and backwaters between Brentford and Kew. The tiny two lipped doorsnail and the German hairy snail thrive in this watery environment enjoying nothing better than a discarded piece of plastic washed up onto the high water line to live under. On the bottom of the river are the mussel beds. Between Teddington and Richmond Lock these are extensive, extending for hundreds of meters – although it would be inadvisable to eat any due to the high levels of dissolved organic matter found in the river. Unfortunately it has recently been confirmed that native mussel populations are in sharp decline (including swan, duck and the depressed river mussel) due to the expansion of the non-native swan mussel that came to the Thames from Russia in the ballast water of cargo ships.
The islands along the river provide a particularly good breeding ground for the grey heron that thrives along this stretch of the Thames. Look across to Brentford Ait, Corporation Island (Richmond) or Isleworth Ait and you will see their nests high up in the trees.
Great crested grebe, mallards, coots, mute swans, moorhens, wagtails and cormorants are also found in increasing numbers. At night owls can be seen along the river.
Recent conservation work has seen the return of the sand martin along the Thames that lives in artificially created banks at Barnes and Twickenham. Careful conservation of riverside habitats is also leading to an increase in the electric blue kingfisher that can now be seen darting along the river. Dolphins and porpoises have been reported as far upstream as Kew and seals are occasional visitors.
Janek finds a slippery eel on the Thames foreshore during November’s draw-off (right)
At low tide long areas of foreshore are exposed particularly downstream of Richmond Lock. Under every stone tiny shrimps and crabs are found. In some places eels can be seen slithering under larger rocks to shelter until the high water returns.
During the summer the riverbank comes alive with all manner of flowering plants that thrive in the wet conditions. Between Teddington and Kew, the river has a high organic content resulting in an abundance of docks and nettles.
Because of this the riverbank needs to be cut several times a year which has seen considerable increases in native flowering plants such as the magnificent purple loosestrife – a key indicator of good ecological health.
The invasive Himalayan balsam plant has now been controlled in many places. Along the freshwater river and areas of calmer water on the tideway; flag iris, water mint, cow parsley, angelica and marsh marigold are found. On the freshwater river kingfisher holes can be spotted, whilst on the tideway, riverbank holes tend to indicate the presence of the invasive Chinese mitten crab.
One of the most specialised wetland habitats are the reed and sedge beds that provide a habitat for a host of wildlife including insects, birds, fish and rare mammals such as water vole and bats. Although 97% of London’s natural reedbeds have been lost, recent conservation efforts have began to reverse this decline.
New reedbeds have been planted at Hampton, Marble Hill, Richmond and Molesey and nearby the Wildlife and Wetland Centre at Barnes is now classified as a Site of Special Scientific Interest.
‘The Tree Line’
At the top of the riverbank trees are found. In particular are ash, alder and willow – many deliberately planted to help stabilise the riverbank from erosion. Along the Arcadian Thames the native white, crack, pussy (also known as sallow) and goat willow are found. The first weeping willow to be planted in the UK was at Twickenham – reputably by Alexander Pope at his Thames-side villa.
Riverside trees need to be regularly maintained so that they do not fall into the river. The traditional way to manage willows is called ‘coppicing and ‘pollarding’. At intervals of between three to seven years the trees are cut to form a thick stump or ‘coppice stool’ that considerably extends the life of the tree, lets in light to the shrub layer and supports a wide diversity of wildlife.
Vigorous new shoots quickly grow up whilst the cut ‘withies’ are used for basket making or planted elsewhere along the river to form new living riverbanks known as ‘spiling’.
The black poplar is the rarest tree found along the Thames. A magnificent example can be found at Ferry Point in Brentford, and between Ham and Kingston the London’s Arcadia project has planted many young specimens propagated from near-by Richmond Park. Ash and alder thrive along the river, particularly in the slower moving freshwater reaches at Hampton Court and Hurst Park.
Other common riverside trees include horse chestnut, lime and the sycamore – a non-native plant that thrives along the Thames. The sycamore out-competes many more important native species. It requires regular pruning to keep it under control. Look high in the trees for the unmistakable balls of mistletoe, particularly in Bushy Park and along the river between Hampton and Sunbury.
Most of the towpaths are artificially constructed to provide some protection from flooding and to allow visitors to walk along the river. One of the consequences of this has been the establishment of damp, areas of woodland and ponds just inland from the towpath that now support a wide range of species including many nesting birds and riparian flowering plants. Good examples are to be found along the Old Deer Park and at Ham.
Grazed Wet Meadows
The traditional habitat along the Thames has for centuries, been water meadows that are either cut for hay or grazed by cattle. Although these meadows are entirely man-made they provide a rich and varied home for a diversity of plant life and are now one of the most endangered habitats in the UK.
Meadows need constant management to thrive and without regular hay cuts or summer grazing by cattle they would quickly succeed to scrub and ultimately woodland. Two of the best places to view these special places are at Syon Park and Petersham Meadow. Look out for flocks of lapwing, redshank, snake’s head fritillary, orchids, adder’s tongue fern, meadow sweet, ragged robin and swathes of buttercups.
Around the edges of the water meadows native hedges are being planted that include species such as holly, hawthorn, dog rose, field maple, damson and sloe. These are managed in the traditional way by layering the branches to form a thick stock proof barrier ideal for nesting birds.
Scrub and Woodland
Areas of wood and scrub are common and provide a magnificent habitat for all manner of species including the song thrush, owls, badger and deer. The River Thames is one of the most important habitats for bats in southern England acting as a huge larder for these nocturnal mammals that feast on the midges and mosquitoes buzzing over the water: a single bat can eat a staggering 2000 in one night.
The bats roost in the old veteran trees in nearby parks navigating their way to the river via the ‘bat super highways’ such as the Ham Avenues that link the river with the open spaces. The Thames is home to seven species of bats including noctule, Daubenton’s and pipistrelle, although their numbers are constantly at threat from development, bad lighting and habitat loss.
Throughout the summer volunteers lead regular bat walks along the river. See events for details for up coming dates.