Legendary Victorian explorer John Speke almost went blind 155 years ago when he battled through desert and jungle to become the first European to gaze upon Lake Victoria - the source of the mighty River Nile.
But it is only now that the source of the Tay has finally been pinpointed, after a detailed, two-year survey of more than 1,000 miles of watercourses in the western catchment of Britain's largest river system.
For centuries, it had simply been accepted by experts that the source of Scotland's longest river was on the slopes of the 3,707ft-high Ben Lui, near Tyndrum. But no-one had ever bothered trying to identity the single source of the complex catchment. The source of the 120-mile long river was finally identified after Victor Clements, the Perthshire area manager for Scottish Native Woods, and two colleagues spent months following the hundreds of miles of main river, tributaries, watercourses and streams that eventually led them 2,300ft up the southern face of the mountain to a tiny lochan, fed by a spring, known as Allt Coire Laoigh.
Mr Clements said Ben Lui had first been identified as the source of the Tay back in 1780. The only reference to the "actual source" of the Tay had been mentioned as Allt na Rund, a small water-course on the slopes of the mountain, in the book Tales of the Tay by Joan Pearson, published in 1975. He said: "We were aware that the source of the Tay was Ben Lui and when we came to surveying the last 100 miles of the project, we decided that the source of the Tay was the logical place to end our journey. But once we started to work out exactly where the source of the Tay was, it was far from straightforward.
"To me, how you find the source of a river is you keep following the watercourses and, every time there is a branch, you take the most dominant one and keep going until you run out of river basically."
He went on: "That's what we did. Three watercourses come down Ben Lui and Allt na Rund, a small watercourse two or three metres wide, had been quoted as being the source of the Tay. Joan Pearson had assumed it was the source because, as it was the most westerly one, it must also be the longest. But we discovered it isn't the longest and it isn't the most dominant watercourse either.
"She was the only person who had stuck her neck on the block and committed herself. We now believe she was wrong."
Mr Clements added: "Following the most dominant water course and also the longest distance from the sea - 120 miles - we identified Allt Coire Laoigh, a small lochan three or four metres square, which must be fed by a spring, as the source."
The survey team state in their report: "We believe that we have redefined the source of the biggest river system in Britain. For the record, we think that, as it is the most dominant tributary and also the longest, the answer is the Allt Coire Laoigh and, as no-one else seems too concerned, we are going to claim credit for redefining the true source of the River Tay.
"Before we left, we buried a small time capsule at the source, including some money and documents relating to this project. If you are ever passing that way and if you can find it, you can help yourself to the price of a fish supper in Tyndrum."
Famous Scots and their African adventures
DAVID Livingstone, the Scottish missionary and African explorer, was obsessed with finding the source of Nile.
He was the first European to discover the Mosi-oa-Tunya ("the smoke that thunders") waterfall, which he named Victoria Falls, on the Zambezi River in 1856. He made the discovery after setting out to trace the source of the Nile but pushed too far west and entered the Congo River systems instead. He died in Africa in 1873 and is buried in Westminster Abbey.
Mungo Park, another Scottish explorer, is credited with being the first European to discover the Niger River, in 1795. He followed the course of the river 80 miles downstream until he was forced to return back. In 1803, he was appointed to head another expedition to the Niger but drowned while trying to flee a native attack. He was only 35.