What is once was
Not much more than 200 years ago there were marshes virtually all the way up the Thames Valley to Oxford and beyond, and there was clean water pretty much all the way from Lechlade in Gloucestershire to Hampton on the western outskirts of London. Data on nitrate levels at Hampton from the Thames provide the world’s longest water quality record and show a steady rise over the last 150 years from near natural levels in 1850 to the highly polluted concentrations of nitrogen we see today. Although there were probably local pollution hotspots, the plants of the river confirm that water quality was much better it is now.
In Berkshire, the loss of nutrient sensitive plants has led the Berkshire county recorder to describe the flora of the river as “one of the most comprehensively degraded [plant] communities in all of Berkshire”.
Away from the main river, there were pollution sensitive water plants and animals scattered in ponds, stream and ditches across the landscape in every little brook, spring and pond. There were probably many more small patches of acid water, and temporary ponds too. For example, around Oxford, where there is a long history of biological recording, there were acid water plants in woodlands like those south west of Oxford at Bagley – now gone. All would have contributed to the variety of freshwater life.
What is it now and why?
The Thames Valley still has many jewels though they are now much more localised. The landscape is now generally much more polluted and clean water has vanished from large areas. Cleaning up of sewage works means that the kind of gross organic pollution that followed the introduction of the water closet is now less prevalent. Raw sewage can now usually only be seen in rivers and streams after heavy storms and the kind of pollution tolerant animal life – a mixture of water slaters, worms and leeches that was once fairly commonplace has now largely gone.
Although the worst has gone, so has much of the best. Now, clean water is largely restricted to isolated ponds and the meadows and grasslands that support them. There is also reasonably clean water in gravel pit lakes, fed by groundwater. But in all but a few streams, and none of the river network, a wide cocktail of pollutants affects our freshwaters, often unseen without special tests.
Salmon are no longer seen in the Thames catchment except as chance strays, and eels, lampreys and other sensitive fish are uncommon. There is still a good run of Sea Trout however. Water Voles have gone from large areas, and the native crayfish have virtually disappeared.
The water plants of clean water – like the bladderworts, Starfruit, several clean water Potamogeton species, like Long-stalked Pondweed, water-violet, Opposite-leaved pondweed and River Water-dropwort are now rarities and it is a real red-letter day when one comes across them.
Amongst the smaller pond animals we know that we have lost other sensitive animals: amongst the water snails, the Little Whirlpool Ram’s-horn snail has gone from Shortwood Common in Surrey, along with the Shining Ram’s-horn, once known from . The acid loving Mud Snail used to occur in the Thames catchment but is now all but gone.