At the edge of this wet region is an escarpment carrying the A303 past the outskirts of Andover. Throughout the year increasing numbers of motorists pull off the road, put on waders, and, filing past the old mill, cast their lines, some for the first time. Last week, in pouring rain, Rooksbury Mill was thriving.
Without most of us being aware of it, angling has become a pounds 1bn-a-year British sport, attracting more than four million participants and employing a further 80,000. Half the anglers are 24 or younger; 10 per cent are female. The pursuit is enjoyed by 'celebrities' such as Jeremy Paxman, Diana Rigg, Eric Clapton and the Queen Mother. It receives increasing attention from broadcasters (last year, BBC 2's Passion for Angling coincided with a Channel 4 series on the same theme). It generates enthusiasms shared by rich and poor alike.
It also makes waves. A cursory cast suggests that anglers are engaged in at least a half-dozen 'wars'. The Campaign for the Abolition of Angling (CAA) has an estimated membership of 200, but it has links with the more aggressive Animal Liberation Front. Claiming that fish feel pain, the CAA has boasted of stoning anglers, damaging their cars, banging dustbin lids to scare fish away, and nagging anglers to distraction, entangling tackle and interfering with fish cages in reservoirs. Nick Carbury, a former British Telecom engineer who runs Rooksbury Mill Fisheries, fears the CAA may inspire 'football hooligans and their Rottweilers' to disrupt the peace of the riverbank.
A second dispute concerns rainbow trout, a non-British species bred here in largely artificial conditions. In Rookbury Mill's tackle shop is a glass case in which a stuffed rainbow, weighing 15lb 12oz and landed locally four years ago, is proudly displayed. Yet it seems the sky's the limit for rainbow: a few miles away, at Dever Springs, Nigel Jackson has already genetically engineered a 30-pounder and anticipates, later this year, a 70lb 'monster' - considerably larger than the record-holding 64lb salmon hooked from the Tay by a woman in 1921.
Mr Carbury, whose clients cast mostly for trout between 2lb and 5lb, snorted: 'A lot of bullshit] Why should anybody want to catch a thing like that?' Richard Colvile, of the British Field Sports Society, was also sceptical. 'It would be quite inedible,' he said. 'Someone gave my wife one of those big slobs. It tasted like mud and was only fit for the cat.'
Fishermen are bitterly divided. The 'purists' want their quarry to be wild and testing. The others don't mind them woolly, providing they look imposing in a photograph or showcase. Peter Tomlinson, former secretary of the Record Fish Committee, says artificially cultivated fish present serious problems for those judging record catches (Mr Jackson's 30lb creature is 5lb heavier than the official rainbow record).
'In 1976 we introduced a 'cultivated' category,' Mr Tomlinson said, 'but it was impossible to operate because you often couldn't decide what the extent of cultivation was. So we reverted to one fish, one record. This is no longer satisfactory because of the demand for large, cultivated catches, so the committee is again deliberating. It may take them some time.'
Two further conflicts are in Scotland. Some clubs, such as the Dornoch Angling Club in Sutherland, have a policy of no Sunday fishing enshrined in their rules and regulations. But demand for brown trout - particularly the wild species of the lochs, renowned for their cunning and willingness to put up a fight - has produced a tug-of-war between hook and Kirk, and fulminations from the Scotsman's angling correspondent ('I deplore Sunday fishing').
At the same time, the Scottish Campaign for Public Angling (Scapa) is battling to establish the 'historic right' of Scots to fish for trout in public rivers. So far its quarry has been elusive: its members were hustled off the Dee by Balmoral 'heavies', and a court banned them from a stretch of the Spey owned by the Gordon Lennox family. Scapa was expected to appeal against the court order, but according to the Scottish Landowners Association last week, it had been unable to pay the first court costs, never mind fund further litigation.
Pollution is probably the biggest battle. Tons of pig slurry, escaping into streams, kill many thousands of fish or cause phosphorous-related algal blooms on lakes. Scientists find that male trout have undergone a 'sex change' because of a high level of female hormones getting into sewage outfalls - the result, they say, of women's contraceptive pills. Male wild trout in Scotland have difficulty distinguishing between their own kind and female farmed salmon which escape into the wild.
Escapes from fish farms have become the subject of angry litigation. Last year, anglers won pounds 10,000 damages from a Wiltshire farm after cultivated rainbow trout got into a river system and ate large quantities of native brown trout. Eight months later anglers won pounds 20,000 from a Yorkshire trout farm for a similar escape. These awards have forced fish-farm owners to exercise care.
'Farming is expensive because you have to own such large lengths of river,' Mr Jackson said. 'But since we have to use 'wild' in the breeding of fish - and to avoid the effects of in-breeding - it's almost true that wild fish no longer exist.'
This weekend, many anglers are switching their tackle from trout to salmon (the salmon season has just begun). Yet Nick Carbury of Rooksbury Mill has good reason not to mind. Parties of managing directors, doctors, engineers and other well-heeled citizens will continue to descend on his property for rainbow trout (all year round) and, from spring, for brown trout. He has 20,000 rainbow and 35,000 brown in his tanks and ponds.
Last week, his middle-aged corporate clients whistled triumphantly at the three-pounders they hooked from his lakes. One of them, a Kentucky Fried Chicken franchisee from Northampton, landed his third, mopped rain from his face and reckoned the day's sport - his first tussle with fish - was worth the pounds 200 (including hotel room and food) he had forked out for it. Another, a property developer, said: 'I caught my first nine years ago, and I remember the joy I felt. I feel it everytime I help someone else do the same.'
For some, joy may be diluted by cost: waterproof hat, pounds 21; waterproof jacket pounds 69; rod, from pounds 45 to pounds 360; rod case, pounds 53. That's not all. Rob Cleminson, a 'corporate entertainment consultant' who took a party to Rooksbury Mill last week, said: 'The most expensive day on the Test would be about pounds 4,200 for eight rods, including champagne breakfast, lunch - the lot.'