Blue on the map is water, but what the map doesn’t signify is how easy or hard the water will be to cross. It might be a simple case of jumping from one bank of a stream to another, hopping across a few boulders in the burn, or swapping boots for crocs and braving the cold for a few metres across a shallow river. Or it may not.

You can get a guide to width, at least, by looking closely at how the water is depicted on an Ordnance Survey map. Streams are shown as a single blue line, where thickness is proportionate to the stream's width, and where the single blue line splits into two, with light blue shading in between, that means the river is more than 8 metres wide.

But regardless of width, in times of heavy rainfall or snow melt the burns and rivers in the mountains of Scotland can present a serious and potentially dangerous challenge.