Physical threats

Issue 4 > Meet the Managers > Water quality issues: Physical threats
Avoid picking up rocks.

Whenever possible, leave rocks where they are: they're somebody's home.

NPS photo.

Habitat disturbance

Please do NOT pick up rocks

A rock is just a rock, right? It may be, except when it's a home. Rocks in streams move on their own during huge floods, but most often they move when people pick them up to search for critters underneath, or form a channel for tubing. No matter how the rocks move, the disturbance can harm the very creatures we value in our streams, including mayflies, caddisflies, salamanders, and fish. Many aquatic macroinvertebrates such as insects, snails, and crayfish use the cracks and undersides of rocks as sheltered homes. Park fisheries biologists also know that some endangered fish lay their eggs under rocks, which provide cover for the parents and protect the eggs. When people move rocks, adult fish flee and predators can find and eat all of the eggs.

It's very easy to avoid picking up rocks—just don't do it! Park biologists and entomologists who regularly study water quality, fish, and invertebrates in streams actually avoid going into the water during the egg-laying time for the endangered fish. If you're in a river, consider the critters that live under each rock and leave the roof on their homes. Choose bigger rivers where you don't have to move rocks into a channel to have fun, or enjoy a lazy float between rocks, knowing that you're keeping a river healthy.
Silty water.

Silty water looks muddy or cloudy compared to most of the Smokies' clear streams.

NPS photo.


What is it?
Silt can be fine soil, sand, rock dust, or ash. Some streams have more silt than others. The Colorado River, with its chocolate milk color, has a lot of silt. Most of the streams in the Smokies don’t. We say siltation is a problem when large amounts of silt fall into our streams, clouding them for days or weeks. Siltation decreases the amount of light available to aquatic plants and animals, can change predator/prey activities with decreased underwater visibility, decreases the dissolved oxygen ("DO," a measure of oxygen available in water for animals to breathe through their gills/skin), and sometimes increases the water temperature by causing more heat absorption.

The Environmental Protection Agency lists siltation as a major threat to water quality, and one that's increasing as construction on land near rivers removes the soil-holding-groundcover. Fine sediment fills gaps between rocks and sand grains (what we call interstitial spaces) that provide habitat for many organisms. It can also clog gills, making it hard for a fish, amphibian, or mayfly larva to breathe.

Where does silt in the Smokies come from?
In any stream, silt can fall gradually or suddenly into water from natural sources such as rock slides, landslides, erosion after a fire, or crumbling stream banks from wildlife use. A small amount of silt comes from these sources, although they are often one-time events and streams can recover.

Biologists are most concerned about siltation from human activities: soil that's trampled and muddy around river access sites, the ripped up ground at invasive hog wallows, development surrounding the park, and arson or accidental forest fires.

Before the Park was a park, people used the rivers to water their fields and their livestock. Sometimes they filled in wetlands—natural filters for silt and other contaminants—and narrowed the streams, making the stream banks tall and firm. This is called channelization: it makes the river flow faster, but it also causes more erosion as the banks crumble into the water. Biologists are working with park vegetation managers to add more plants to these streambanks, especially in Cades Cove, to slow the water flow and cause less erosion.

What do we do to stop siltation?
Siltation from human actions is tricky to stop because it doesn’t come from one main source. Posting signs to use only one stream access, using durable surfaces for beaches/access points, building campfires in campgrounds or fire rings only (to prevent a human-caused forest fire in an area that could erode), and supporting park efforts to keep invasive species—such as wild hogs—out will help.


Did You Know?