Rivers, streams and lakes – flora and fauna in Dorset’s rivers
Colin Varndell looks at the flora and fauna to be found in Dorset's rivers
Published in February ’13
We all have romantic ideas of riverbank wildlife being like Wind in the Willows, and there definitely is something very magical about a stroll along one of Dorset’s rivers on a summer evening. But for the creatures which live there, this habitat is little short of a battlezone, as the water which attracts so many fascinating creatures is also a magnet for their enemies. On top of this, they exist in an environment that can be suddenly transformed by rain from a gently gurgling stream one minute to a dangerous raging torrent the next.
Dorset’s rivers, streams and lakes are teeming with wildlife ranging from the tiniest invertebrates to fish, birds and large aquatic mammals. The food chain begins with the lowliest of invertebrates, the aquatic nymphs and larvae. Many species of flying insect like mayflies, dragonflies, mosquitos and stoneflies for example begin their lives in fresh water. At the aquatic stage they may feed on smaller organisms or in turn be food themselves for fish or predatory invertebrates like dragonfly nymphs.
Dragonflies and damselflies have evolved to take advantage of two completely different habitats – under water at the nymph stage they can live for up to three years, before emerging to prey upon gnats and midges in flight. One of Dorset’s special dragonflies is the scarce chaser. As its name suggests, it is not a common insect and is on the Red data list of endangered species. In East Dorset, though, it is relatively common, breeding on the Frome, Stour and Moors rivers. The beautiful demoiselle is found on quicker-moving streams and rivers in the south and west of the county, while its close relative – the banded demoiselle – favours Dorset’s larger, slower waterways like the Frome and the Stour.
Many specialist waterside plants thrive on our riverbanks and stream ditches, like yellow flag, great willowherb, meadowsweet, purple loosestrife, water forget-me-not, mimulus and watermint to name just a few. However, the rapid spread of the non-native Indian balsam threatens native flora by forming dense stands that block out the light. Its spread across Dorset has been swift and it is now seen in huge drifts crowding the banks of many rivers and streams. Another alien wild flower occurring along Dorset’s riverbanks is giant hogweed which can grow up to three and a half metres in height with flower heads measuring 45 centimetres across. This enormous umbellifer can be seen along the river Brit near Beaminster and also along the Allen in the north of the county.
Wherever there is unpolluted water there are fish, which in turn attract predators of both avian and mammalian kinds. The North American mink has been the scourge of many of Dorset’s rivers after escaping from fur farms in the seventies. The mink is just as capable at killing small mammals or birds as it is devastating fish populations, and it has been held responsible for the drastic decline in water vole populations across the county.
The recovery of the otter in Dorset, after it was driven almost to extinction in Britain, is due to improved water quality and the special protection which is now afforded to it. Recently, there have been regular sightings of otters with cubs on the river Brit. This is not only good news for otters in west Dorset but also good news for water voles. Otters do not tolerate mink and recently there has been a marked decline in the number of mink records. Hopefully, with otters firmly established on our watercourses we will see fewer mink and an increase in the watervole population in the near future. All birds rely on water to drink and bathe regularly. However, there are some birds which are inextricably linked to rivers and streams. Due to the hillier topography in the far west of the county, rivers and streams tend to flow faster than in the east. These fast flowing watercourses support dippers, which feed on aquatic invertebrates and habitually venture underwater in search of food, hence the name.
Where there are dippers there are usually also grey wagtails because the habitat suits both birds exactly. The grey wagtail is often misnamed the yellow wagtail on account of its predominant yellow colour; it is the grey head, though, which gives the bird its name. Grey wagtails are extremely vocal in spring and summer, standing on rocks to deliver their penetrating song with their long tails constantly wagging.
Little egrets used to be rare visitors to Dorset, but since the mid 1990s they have become permanent residents. Little egrets now breed at a number of sites in the county and may be seen fishing in most rivers, although there are some particularly favoured sites for egret spotting like from the bridge at White Mill on the Stour.
The common sandpiper is a spring and autumn visitor to Dorset’s waterways as it drops in for refuelling on its way to and from breeding grounds. It breeds in afforested areas in northern England and Scotland, overwintering in north Africa.
The water rail is present here all year round, although you may not think so as this is one of our most secretive birds and is much more likely to be heard rather than seen. Usually, the water rail remains hidden in vegetation. Oddly, it is most often seen during hard weather when it will venture out onto ice in the open.
My own interest in photographing nature was triggered when I first watched kingfishers on the Mangerton river near Bradpole. I was not expecting to see kingfishers that day, although since, with many years of kingfisher-watching experience I would expect a sighting of a kingfisher on any of Dorset’s unpolluted rivers and streams just by sitting still and waiting. Kingfishers do not appear to take much notice of humans who remain still. I was transfixed by the sight of this striking small bird when it alighted on a fencepost near where I sat. The bird stared intently into the pool beneath and within seconds splashed headfirst into the water, returning to the post with a stickleback. This is one of the many fantastic experiences that any of us can have, simply by taking the time to sit by one of Dorset’s rivers or streams for a while. For me, this one experience changed my life.