IT is Scotland's highest gorge and is normally seen only from the safety of a suspension bridge which offers visitors panoramic views of the magnificent waterfall plunging into a river far below.

But despite its remote location and inaccessibility, the 197ft high Corrieshalloch Gorge in Wester Ross has become overrun with invasive foreign species like rhodedendron and Japanese knotweed.

Now the National Trust for Scotland has gone to extreme lengths to get rid of the problem by abseiling down the steep sides of the gorge and also enlisting the help of 'gorge scramblers' to root out the invasive species.

Conservation workers have abseiled into the gorge to identify spots where the species have grown and, depending on the size of the plants, have injected or sprayed them with measured doses of herbicide.

In addition, Scotland’s ‘gorge scrambling’ community who are regular visitors to Corrieshalloch, have gone into areas that might not otherwise be accessed by regular surveys and have been able to spot colonies affected.

Gorge scrambling sees people making their way up or down a mountain river course, jumping into pools, and swimming under waterfalls to experience nature in a different and more personal way.

Japanese knotweed, in particular, has a reputation for being difficult to extract, spreading quickly and surviving for long periods even when dormant.

Both species are also notorious for reducing biodiversity, causing the loss of local flora and fauna.

Rhododendrons block out sunlight and prevent other plants from growing, while Japanese knotweed can loosen river banks with its aggressive root systems.

Rob Dewar, Nature Conservation Advisor (North) at National Trust for Scotland, said: “Both Rhododendron ponticum and Japanese knotweed are a very serious threat to the rich diversity in the gorge.

"These plants are in a very extreme place to access, but we need to take thorough measures to make sure we identify the areas affected and remove the invasive species.”

"The gorge scrambling community is acting as our eyes in the difficult depths and corners of Corrieshalloch – we’re also working with them to develop sustainable adventure tourism at the site.

"We want to use their knowledge as much as we can to tackle colonies of the invasive plant species that may otherwise be missed – they can make a real difference to the future of the gorge, all while doing what they love".

But how the species ended up in the gorge remains a mystery.

It is situated just off the main A835 Inverness to Ullapool road around 22 miles south of the Loch Broom ferry port and there has never been a railway to the town.

Back in the nineteenth century, when Victorian engineers were designing the latest in transport technology engineers imported Japanese knotweed to stabilise ailway embankments.

It is a plant that typically colonised volcanoes in Japan and was imported to hide the newly-built embankments on the ver expanding railway system.

However, since then it has spread uncontrollably across the UK and brought misery to home-owners and prospective house purchasers.

It can crack tarmac, block drains, undermine foundations and invade homes and its presence can be enough to cut a property's value by up to 20%, or prevent a mortgage lender approving a loan.

Rhododendron was imported as a seed in the late 18th Century and was widely planted across Britain.

However, when it is grown in suitable conditions the plant thrives and spreads quickly with each flower head producing up to 7,000 seeds.

Due to its quick growing nature it becomes a dense shrub, covering ground which stops native plants from growing.

As such, areas where Rhododendron is allowed to establish have the capability to collapse the food chain from the ground up, eliminating insect food plants and even decreasing the numbers of earthworms in the soil.

Conservationists hope the extreme measures undertaken will protect Corrieshalloch Gorge’s diverse range of native trees which include aspen, hazel, rowan, birch, pine, and wych elm.

It is also home to a large number of mosses, lichens and ferns along with a variety of wildlife which depend on its flora, such as red squirrels, woodland birds, ravens, and golden eagles.

Corrieshalloch Gorge sees the Rover Droma plunge 151feet down the Falls of Measach and through the mile-long ravine.

It has been owned by the NTS since 1945, but the suspension bridge to allow visitors access was built in 1874 by John Fowler, the engineer responsible for the world’s first underground railway and joint chief engineer on the Forth Bridge.

Mr Dewar added: "The control of Japanese knotweed and rhododendrons is part of a larger project with other landowners to protect biodiversity on this river catchment.

"The work at Corrieshalloch is a great example of the extreme lengths to which we will go to protect Scotland’s natural heritage, preserving our history and culture for current and future generations to enjoy.”