Engineer David Mummery says tidal power could change lives in coastal communities
In a secret location in the Highlands of Scotland, there's a fast-flowing river that's the key to understanding the massive power of water.
It's where engineer David Mummery found himself more than a decade ago.
With a length of cord tied tightly across the river, he swam out, gripped firmly, and let the unstoppable current rush over as he sunk his head below the surface.
"As an engineer we do the maths and stuff," he says, "but sometimes you can get a lot more from actually touching the water and feeling it".