From the Eno River Association:
Most parks encourage visitors to follow the principles of Leave No Trace, but there is a lesser known aspect of Leave No Trace related to lesser known critters. In rivers, the rocks, gravel and sand provide habitat for a great diversity of aquatic life forms. Plants that grow on the rocks clean and oxygenate the water. We all love clean water! Tiny aquatic insects like mayflies, stoneflies, and caddisflies often spend a part of their life cycle attached to submerged rocks. Crayfish too like to hide under rocks, as do the rare salamanders called Hellbenders that live in the western part of the state.
Rock stacking or ‘cairn’ building can crush or displace these animals, or leave them out to dry and die. They depend on us to Leave No Trace by leaving the rocks in the river! Next time you head to the river, bring along a book or a journal instead, so we can let our aquatic neighbors live in peace.