Tower and Town, September 2022 (view the full edition)Nature NotesChalk streams: A precious water runs through Marlborough- the Kennet, a chalk stream. There are only 210 in the world, 160 in Southern and Eastern England. In Wiltshire we have a stretch of the Avon, and its tributaries the Ebble, Nadder and Wylye, as well as the River Kennet and its tributary the Dun. Chalk streams are rivers that rise from springs in landscapes with chalk bedrock. Since chalk is permeable, water percolates easily through the ground to the water table and the streams therefore receive little surface run- off. The water in the streams contains little organic matter and sediment and is generally crystal-clear, the beds generally composed of clean, compacted gravel and flints, which are good spawning areas for game fish. Since they are fed primarily by aquifers, the flow rate, mineral content and temperature range of chalk streams exhibit less seasonal variation than other rivers. All have been modified in some way, usually for milling, fishing, irrigation or watercress beds, but despite weirs, impoundments and abstraction, the best chalk rivers still support a fine aquatic flora and a diversity of invertebrates and fish, including bullhead, brook lamprey and crayfish. They are mildly alkaline and contain high levels of minerals: in addition to algae the streams provide a suitable habitat for white-flowered water-crowfoot, water-starwort and watercress. John Hounslow has been river-keeper on a stretch of the Kennet flowing from Elcot to Stichcombe for over 40 years, one of five keepers covering the waters as far as Newbury. He undertakes many tasks to keep the 34 members of the Savernake fly-fishing syndicate happy: bank stabilisation, coping with poachers, trespassers, canoeists and swimmers, brown trout restocking, weed-cutting with a hand-scythe and discouraging invasive species such as Himalayan balsam, American crayfish, mink and cormorant. ARK (Action for the River Kennet) has done much to protect the river from the export of water to Swindon and improve water quality: volunteers have taken on some of John's onerous tasks. In this mostly dry year water levels are worryingly low and the lack of invertebrates and variable water quality makes hard work for the fisherman, who pay a high price for their sport. If the numbers of nymphs and olives are low, trout are less inclined to go for imitations on a fly-line. The anglers pay the highest prices in the mayfly season, when fish lose their inhibitions and go crazy when the insects hatch: suddenly fly-fishing is easy, giving rise to the term "duffers fortnight." A dipper spent most of the winter on the Kennet at Town Mill, Marlborough: its presence there is an indication of the quality of the aquatic environment. I was sorry to see a Waitrose trolley half-submerged nearby, making me wonder if people know how special a chalk stream is.  Robin Nelson |