No such feats are possible today. Fishing on the Wye has gone into a disastrous decline, especially in the past decade. During the 1980s declared catches of salmon were running at 6,500 per annum, but by 1997 and 1998 years they had fallen to only about 800. Landowners, and owners of fishing rights, kept hoping that a miraculous recovery would somehow occur, and were extraordinarily slow to react. But now, under the energetic leadership of Dr Stephen Marsh-Smith, a dentist who works in Bristol, they have formed the Wye Foundation and at last begun to take remedial action.
Already, the national Environment Agency has enacted a by-law which obliges anyone who catches a salmon to return it to the river. Yet the owners believe that far more radical measures are needed. The foundation is seeking to buy off the commercial netsmen who take heavy toll of fish entering the estuary. At the same time, it is working to improve the habitat in which salmon and brown trout breed in the upper reaches of the river. Individual owners have been clearing dead wood from tributaries and cutting fish-passes around rock falls so that salmon can go farther up-stream to spawn. But the main initiative is the Wye Habitat Improvement Project, which was launched last year with money from the European Agriculture Guidance and Guarantee Fund, supported by other organisations.
The principal targets for restoration are four of the Wye's important tributaries, which wind out of the hills in Central Wales: the Clywedog, the Edw, the Masteg and the Cammarch, all of which have become seriously degraded over the past half century. Along many stretches, alders have grown so thick and tall that they shut out the light; sheep and cattle have eaten the verges to the bone so that no vegetation is left to give fish cover; and in countless places the banks have been trampled into the water, allowing erosion to take place, and increasing siltation.
The remedy sounds simple: to keep grazing animals away from the banks by means of fences, and to coppice the alders - that is, to cut the trees off at the base of the trunk, so that in time they will shoot again. Yet to put the plan into action has taken extensive planning and diplomacy.
On 10 miles of Clywedog Brook and its own little tributary the Bachel, the project officer, Philip Ferguson, first had to persuade 30 farmers that the scheme would be in their interest. Beginning last summer, he explained to them that although all species, including salmon, will benefit from the work, the fish that stand to gain most are brown trout. If things work out, wild trout fishing, which used to be much prized in the area, could again earn useful income. As he says, "Getting money back into the rural economy is one of our main aims."
In the event, 27 of the farmers agreed to let the work go ahead, and the other three allowed monitoring of their stretches of the river. All concerned cooperated, lending tractors, trailers and quad-bikes and taking a close interest in progress.
The landowners, however, were only the start: Mr Ferguson also had to obtain the agreement of all the statutory bodies involved. "First I had to mark every single tree that we wanted to fell," he said. "Then along came someone from the Countryside Council for Wales who specialises in lichens. Then someone interested in bats. Then someone studying dormice. Every tree had to be discussed by a whole posse of visitors. Then we had to estimate the trees' volume and apply for a felling licence. While waiting for the licence we had to notify the Environment Agency and the CCW. Eventually we got the licence, which every farmer had to sign."
The complications did not end there. Every square foot fenced out of a field meant, in theory, the farmer might have lost that amount of grazing. Therefore his hideously complicated IACS forms, which he is obliged to fill in every year to obtain European Commission subsidies, might no longer be accurate.
In spite of the bureaucratic nightmare, Louis Macdonald Ames, habitat manager for the project, and his team of seven have coppiced hundred of alders, whacked in more than 2,000 fence posts, and put up 260 50-metre rolls of sheep netting. The fences are beautifully built and extremely strong - as they have to be to withstand winter floods - and already striking changes are apparent inside protected areas. Grass, brambles, nettles, thistles, reeds - all are growing in abundance, providing not only cover but rich insect food for juvenile trout and salmon.
In some ways history is being repeated, as in the old days farmers used to coppice the alders for charcoal (used in the manufacture of gunpowder), for wooden clogs and primitive land-drains. The new team is also using logs nailed into the bed of the river with six-foot steel bars to make revetments (barriers) across bays that have been eroded from the banks - again, a practice common in earlier times. Silt, settling behind the walls of wood, gradually fills in the hollows and re-establishes the line of the bank.
Only time can show what effect all this work will have. But the team are encouraged by the results of a similar scheme carried out on the Piddle, a chalk stream in Dorset. Down there - admittedly in a more fertile part of the world, with a kinder climate - the population of juvenile trout has increased sixfold in only three years. If anything like that happens in the lovely but unforgiving hills of Radnorshire, there will be much jubilation; but even if the present project does prove successful, years of all-round effort will be needed to return the Wye to its former glory.