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It's a hot day, the river is too shallow to cool off in, and a few rocks would make a perfect soaking pool. The little engineering project seems harmless. It can do more harm than good — to the animals living under those rocks and to the river itself, even well upstream.
Gauley River National Recreation Area. Credit: National Park Service.
What rivers do
- Clean water. The sand and rock of the riverbed (the substrate) filter and purify water, and the current keeps sediment and pollutants from piling up in one place.
- Flood control. It sounds backwards, but rivers carry rain and snowmelt away. The river itself may flood, but the land around it is spared much of the extra water.
- Habitat. Twists, turns, fast and slow stretches and different kinds of riverbed create habitats for all kinds of living things. Rivers are among the most biodiverse ecosystems, with some of the highest concentrations of threatened and endangered species.
Who lives under the rocks
Many river animals depend on a particular mix of current and substrate. Trout and salmon lay their eggs among the rocks on the bottom, where the rocks help oxygen reach the eggs. Salamanders and aquatic invertebrates shelter under rocks from predators and the current.
A salamander on a stream rock in Great Smoky Mountains National Park. Credit: Mike Bell, National Park Service.
Stacking rocks can take away that shelter — and the extra weight can crush small, often camouflaged animals underneath. Leave No Trace practice near a river is simple: leave the rocks where they are.
What happens to the water
| Change | Effect |
|---|---|
| Rock dam | Raises the water level, lets abnormal amounts of sediment build up, slows the flow |
| New channel | Lowers the river's water level, speeds the flow upstream, increases erosion |
Either way, changing a river's character reduces the variety of habitats and strips away some of what makes a free-flowing river a thriving ecosystem. Less than one percent of U.S. rivers flow free of human-made obstructions; the country protects some of them for present and future generations as Wild and Scenic Rivers.
Bluestone National Scenic River. Credit: National Park Service.
How to help
- Enjoy rivers' natural beauty and practice Leave No Trace.
- Leave river rocks in the river.
- Don't alter the flow — no dams or new channels, especially near a river outlet.
- Join a river cleanup.
- Fish responsibly.
- Find a river near you — and pass on what you learned.
Sources
Based on "I Didn't Know That!: Keeping Rivers Wild," National Park Service; a work of the United States government in the public domain.
Лицензия: CC0 1.0 (общественное достояние) · По материалам www.nps.gov
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