The word cairn is derived from the Scottish Gaelic meaning stone man. It can invoke images of faith, purpose, and spiritual journeys. Cairn-building is a common activity in the backcountry. It's easy to understand why people are drawn by these small piles of flat stones that can be stacked like children's blocks. A hiker with aching shoulders and black insects buzzing around her ears will try to choose a rock that is the perfect combination of flatness width, tilt, and depth. After a few misses (one too big, one too small), a purist will select the stone that fits perfectly into place. The second layer of the Cairn is now complete.
Many people are unaware that cairn construction can create negative environmental impacts particularly when it is constructed near water sources. When rocks are removed from the edge of an ocean, a lake or pond, they can disrupt the ecosystem and eliminate the habitat for microorganisms which provide the food chain. The rocks could be removed from the edges of a pond, river or lake by erosion, and end up in places where they may harm humans or wildlife.
Cairn building should be avoided in areas that have rare or endangered mammals, reptiles amphibians, plants, or other species or where the water is trapped under the rocks. If you construct a cairn on private land it could be in violation of federal and state regulations that protect the land's natural resources and could result in fines or even a detention.