It is puzzling that we should be told to be more considerate towards our rivers at a time when we have never, on the face of it, treated them better. As long as they behave themselves, by not bursting their banks or offending our sense of smell, we look upon them with a glow of affection.
They are the backdrop to many of our favourite leisure pursuits. We bathe in their water, or sail, punt or putter-putter along it. We sit motionless with fishing rods along their edges. We walk and laze on their grassy banks, watching the ducks and the water-birds. None of that places undue strain on the river's precious resources.
In the past, though, our relationship with rivers has been more ambiguous. From the earliest times we took terrible liberties with them. We have used them to supply food, drink and washing facilities and as key transport links.
When the Romans came to Britain, they chose a site for their capital where no earlier settlement existed because it was the most easterly point where the Thames, the main entry point from Europe, was narrow enough to bridge. Within a century or two, London had become one of the most important commercial ports in the western world.
The first London Bridge, an impermanent wooden structure put up by the Romans, was the most significant attempt until then to tame Britain's rivers and exploit them to enhance people's lives. Until a river is bridged, it is an effective divide between territories, to be crossed only at the river's whim, at the right state of the tide - and even then with difficulty and danger.
After bridges came dams, weirs, water mills, docks, locks, embankments, flood barriers and much else; devices to change the geography of the river, even to divert its course, to suit the convenience of the populace. When the Romans came, for instance, the Thames was twice as wide as it would become after Bazalgette built his embankment in Victorian times, and a lot shallower.
It is a mistake, though, to believe that without human intervention our rivers would have remained unchanging features of the landscape. They are in a constant state of flux on their own account. Before the ice age the Severn flowed north from Shrewsbury, not south, and the Thames probably reached the sea much further north than it does today. More recently, many rivers have changed course through erosion or freak weather.
Today's concept of the river as a source of delight rather than as a purely practical amenity has its origins in the 17th century when popular pleasure gardens such as Vauxhall and Ranelagh began to be built along the banks of the Thames. Soon landscape painters were creating romantic riparian scenes.
Before that, noblemen built their splendid riverside palaces not for the views but for pragmatic reasons, so as to be close to their main communications link. Even then, several hundreds of yards of garden would normally separate the house from the river, with its busy traffic and the stench of raw sewage rising from the water. As early as 1357, Edward III complained about the "dung and other filth" on the banks of the Thames at low tide, and the consequent "fumes and other abominable stenches".
If rivers were undesirable neighbours even then, they became almost unlivable- with when the industrial revolution took hold. Riverside sites were ideal for nearly all kinds of manufacturing because materials and finished goods could easily be transported while water was on hand for driving the machinery. Potteries, tanneries, flour mills, breweries, shipyards, arsenals and factories of every kind were established beside rivers up and down the country. Industrialists extracted fresh water and replaced it with polluted effluent, without a thought for any long-term consequences.
Some of the country's worst slums, in the dock areas of large cities, backed on to the rivers. Legislators became concerned only when the problem was brought literally to their doorstep. In the Great Stink of 1858, the smell at the Palace of Westminster was so unbearable that its windows had to be draped with curtains soaked in lime solution. Soon afterwards Parliament authorised the building of Bazalgette's embankment and sewer.
As for industrial effluent, steps were taken to control it but the problem was not wholly solved until the changing economy meant that riverside industry faded away of its own accord. With transport shifting to the roads, there was no longer a need for factories to be by a river, or for the extensive docks that had been established in Liverpool, London and elsewhere.
Former warehouses and factory sites were converted into riverside apartments (with odour-free vistas), hi-tech offices, leisure centres, marinas and riverside walkways. The water became, if not pellucid, at least tolerably clean.
Almost every year, though, floods in winter and spring remind us that our rivers are never to be taken for granted; the present drought reinforces the point. Only through careful maintenance and husbandry will the river gods continue to do what we require of them.
It is an irony. We have cleaned up our rivers until many, for the first time in centuries, are good enough to drink: lo, we are told we must drink them only in moderation. Our offence is not that we are injuring the rivers, but are stealing their basic resource.
A depleted river could one day become no river at all, turning a once fertile plain into a desert. Unless we can find still more ways of reducing our demands on him, Ol' Man River may not always keep rollin' along.
The writer is the author of `London's River' (Pavillion pounds 16.99).Reuse content