The streams and waterfalls that had once graced his ancestors' land in Alston, Cumbria, had been buried by the deposits from more than a century of lead mining.
Now, after 27 years of painstaking work, Mr Johnston and his family have restored Thortergill to its former glory and made it a haven for stoats, red squirrels and other wildlife.
Mr Johnston, now 59, said: "The Johnston family used to own what was called the Shield Hill Estate. Thortergill was part of that estate and it was sold to a lead company in 1780. The mine was opened in 1823."
The miners transformed the landscape. The stream that flowed through the ravine was covered with a dry stone culvert so that the workers could reach the lead in the sides of the ravine from a solid base.
Mr Johnston explained: "As they exploited the mine they dumped the waste on top of the culvert and along its sides so that Garrigill Burn [the stream] became buried. The valley, which was V-shaped, became U-shaped. By the time the mine had closed the ravine had been virtually destroyed."
With the miners came an aqueduct system, horse-drawn carts, railway tracks and an access road. "They were civil engineering geniuses. All this activity went on here for more than 100 years," said Mr Johnston, who explained that the river, which was buried beneath 20 feet of rubble, became a pond when the culvert collapsed under the strain of the mining waste.
Determined that Thortergill would one day be restored, Mr Johnston's uncle bought back the land from the mining company in 1939.
He converted the miners' buildings into a cottage where Mr Johnston now lives with his wife, Jennifer, and sons David and Andrew.
"My uncle had no childrenand he made it known very early on that I was going to succeed him," Mr Johnston said. "I remember looking at this place as a boy, wondering how on earth I was going to restore Thortergill."
Using only his own money, Mr Johnston, who sold industrial products on Tyneside for a living, set about removing the collapsed culvert, re- creating the stream and planting new trees and flowers. Because lead sulphide is insoluble, pollution was not too much of a problem, he explained.
Mr Johnston, whose project is featured on BBC Radio 4's Changing Places on Friday, said: "Our objective was to do all the work we could on our own. When you open the door in the morning and see the birds and animals all waiting for their breakfast it makes it all worthwhile."
The Johnstons now run a tea shop and a blacksmiths' forge that, ironically, is a legacy from the mining era. He said: "My sons are blacksmiths and use the forge which was on the mine for 100 years."Reuse content