WILD: Keep it wild, folks, even streams and rivers. The National Park Service has a series called “I Didn’t Know That!” where they explore common things that people might do, thinking they were harmless.

Damming up a stream for a swimming hole is one of them.

“Rivers provide more than just a fun place to play. They serve as an active provider of clean water. The sand and rocks (substrate) at the bottom of a river help to filter and purify the water. The flow of the water itself also keeps sediments and pollutants from building up in one spot.

“Rivers also prevent floods! (What?!) Rainwater and snowmelt need a place to go. While it may seem counterintuitive, rivers provide a perfect system for that water to go, minimizing the impact to surrounding areas. While the river itself may flood, the places around it will be less affected by the extra water.

“Rivers naturally twist and turn, with different sections of faster or slower moving water. The variety in water flow combined with different kinds of substrates on the river bottom creates diverse habitats for all kinds of living things.

“Many organisms that live in rivers rely on specific combinations of water flow and substrates, like sand and rock, to survive. Fish, like trout and salmon, lay their eggs among the rocks at the bottom of streams. The rocks help to improve oxygen flow to the eggs. Other animals, like salamanders and aquatic invertebrates, often rely on river rocks for shelter – both from predators and from the current.

“If we stack rocks in rivers, we may be removing important sources of shelter for these species. We might also accidentally squish small, often camouflaged, animals underneath the weight of the extra rocks. Best practice for leaving no trace near a river is to leave the rocks in their natural places.”