grounds.
The nymphs, or first larval stages of mayflies, are also adapted to very particular conditions. Some nymphs have specially shaped heads and legs, so that, when facing the current, they are pushed against stones into which they fit, and which save them from being washed away – certainly a case of going with the elements! The yellow may nymph is best adapted for rough boulders, while the marsh brown nymph fits against smooth stones, upon which its gill-like plates press down, thereby creating a vacuum. While some species are streamlined for fast flows, others are burrowers and bottom-crawlers. The claret dun nymph is at home in slow, peaty streams. It is peat-coloured, and its gills both camouflage it by breaking up its outline and enable it to breathe in still water. The blue-winged olive nymph lives among weeds such as water crowfoot. It is neatly shaped to lodge in close-packed vegetation, from which it can be in close contact with the fast-flowing oxygenated water it requires.
Reed buntings and common reed.
The culmination of all this unseen evolution on the river bed is one of the great phenomena of the English countryside, once seen, never forgotten. This is the day in the life of the mayfly. Very punctually in mid-May, the nymphs will rise from the bed of the river and hatch through a final nymph stage known to anglers as ‘duns’. Then, when the air is still, the elegant adults, the ‘spinners’, float upwards in their thousands and perform their mating dance. This is the sight that stays with even the casual observer. The gauzy tides of swarming males, waiting for the females, rise and fall as if on invisible yo-yos. Having mated, grey clouds of females glide to the water, lay their eggs, and die. With all the poignancy of a Shakespeare sonnet, it is over in the space of a summer day, until next spring.
When I consider every thing that grows
Holds in perfection but a little moment.4
The life of a river has nothing to show more resonant of changeless change than the life cycle of the mayfly, a genus known even in the dry language of science as Ephemera.
Yet the return of the mayflies is no longer as inevitable as the return of May. They are steadily declining in many rivers, and have vanished from others. Pollution and the removal of riverside hedges have played their part; but above all, dredging and drainage have ironed out the varied bed conditions of gravel and silt to which the larvae of these and many other insects were so minutely adapted.
The otter, sliding up a river like a sleek cat and whistling to its mate under the moon, is truly king of the waters, and the presence of otters on a river system sets the final seal of well-being on its wildlife. The otter has captured popular imagination ever since the classics of Henry Williamson and Gavin Maxwell. It achieved tabloid status in April 1985, when it was on the front page of the Daily Mirror’s conservation shock issue; and, as a symbol of wildlife under threat, it is a sure money-maker for such causes as the World Wildlife Fund. The fact that people will give money to save the otter, a nocturnal animal whose presence is detected even by full-time otter survey teams only by its tracks and droppings, is the best answer I know to that mean-spirited and illogical argument: ‘What’s the use of saving it, if I can’t see it?’ It was enough simply to know that otters were out there somewhere. Alas, no longer. In 1977 leading conservationists produced a report showing that the otter had declined with disastrous suddenness.5 Whereas otters were present, even common, throughout the country in the 1950s, they are now abundant only in the extreme north-west of Scotland, leaving core populations in Wales and the West Country, and a dwindling interbred group of individuals in East Anglia. Hunting, disturbance, and pesticide residues had all played their part; but the major culprits were river boards and their successors which scoured the banks of undergrowth in which otters lay up during the day, and felled the mighty riverside trees, such as ash and sycamore, in whose buttress roots otters made their holts. Since 1977 otter hunting has been illegal, and the ban on the pesticide Dieldrin is starting to have a beneficial effect. But the many miles of treeless river inhibits recolonization by otters, and even in the 1980s there have been cases of water authority workers felling known otter holts.fn4
THE CULTURAL HERITAGE OF RIVERS
It is not only wildlife that is at stake. Rivers represent a cultural heritage as well. Through aeons of geological time, rivers, in the wake of glaciers, have helped shape the very structure of our landscape. When civilization arrived, rivers shaped human history, and humans, in turn, began to shape the rivers.
From the time that the tribal Belgae and then the Romans invaded England, rivers dictated the positions of many towns and villages. It is believed that the great bluestones of which Stonehenge is constructed were floated up the Wiltshire Avon. Christianity came to England up a river, when St Augustine and his forty monks travelled to Canterbury up the Kentish Stour, ‘singing all the way’. Rivers were also highways of terror. The sleek hull of a Viking boat was specially designed to be shallow enough and narrow enough for use on navigable rivers, along which Norsemen brought fire and the sword. Along the waterways was carried most of the stone required to build our medieval cathedrals. When Whittlesey Mere was drained in the 1850s, a heap of dressed stone was found at the bottom of the lake, evidence of a medieval boating accident. It is thought that the cargo was destined for Crowland Abbey.fn5
In the eighteenth and nineteenth centuries the harnessing of water power for mills, and river navigation, interlinked with a new system of canals, laid the foundation for the Industrial Revolution. Through all this change, rivers have continued to flow; but, for those who have eyes to see, the imprint of each generation remains, varying and concentrating the character of each stream that flows past our homes and our lives.
A good example of this is the water mill. The Romans introduced water mills to England, and the Domesday Book records as many as 5,624. All but a hundred of these mill sites can still be accounted for. Up and down rivers and brooks, the remains of some of these and many later water mills can be seen. In some cases, magnificent buildings, complete with all their machinery, still stand. Elsewhere there are just clues to former occupancy: foundations, a silted millrace, or the remnants of a weir, as described by Edward Thomas:
Only the idle foam
Of water falling
Changelessly calling,
Where once men had a work-place and a home.6
All this human interference with rivers, the building of millraces and millponds and, in some cases, quite major diversions of watercourses, did not destroy the essential character of rivers. On the contrary, it added to it, and not just in terms of the quality and character of the landscape, but also from the point of view of the wildlife. A tumbling weir creates the localized conditions of an upland brook wherever it crosses a silty lowland stream. Here grow the willow moss and liverworts found again in abundance only towards the sources of a brook. In the highly oxygenated water below a weir swim the little fish not known for nothing as the ‘miller’s thumb’: the flattened head of the fish was often compared with the thumb of the miller, worn it was said from testing the flour. Perhaps the loveliest of upland specialists associated with weirs and mill sites is the grey wagtail – grey in name, but not in appearance, with the flash of his canary-coloured chest. The grey wagtail nests in ledges and crevices of rock upstream, and finds a similar home in the crumbling walls and vertical structures of water mills. Edward Thomas may not have known that he was also making an ecological point when he pinned down so precisely the atmosphere and feel of these places:
Attractive colonizers of the mill weirs. Grey wagtail and the delicate
