How Sediment Causes Pollution

Waterway running brown from sediment runoff next to a field of crops.

Natural Resources Conservation Service — New Mexico, U.S. Department of Agriculture/Wikimedia Commons/Public Domain

According to the Environmental Protection Agency, one of the three major sources of water pollution in streams and rivers is sediment.

What Is Sediment?

Sediment is fine-grained particles like silt and clay, generally occurring as a result of soil erosion. As rainfall washes away bare soil or a stream erodes a muddy bank, sediment makes it into waterways. These fine particles occur naturally in the environment, but problems arise when they enter aquatic systems in larger quantities than they would naturally.

What Causes Soil Erosion?

Soil erosion happens anytime barren soil is exposed to the elements, especially after a lot of vegetation is removed. Plant roots are very effective at holding back the soil. A common cause of erosion is road and building construction. During construction, soil remains exposed for extended periods of time. Silt fencing, made of a textile held up with wooden stakes, is often deployed at construction sites as a sediment containment measure. 

Agricultural practices lead to long periods of time when vast expanses of soil are left barren. In late fall and winter, millions of acres of farmland are left exposed to the elements. Even during the growing season, some crops do not protect soils adequately. Corn, most notably, is planted in rows 20 to 30 inches apart with long strips of barren soil in between.

Forestry practices can also lead to erosion, especially on steeper slopes. The removal of trees does not necessarily expose soil directly, and careful logging operations can keep erosion to a minimum. However, machinery can damage low-growing vegetation. High-use areas, like logging roads and landings, certainly leave the soil unprotected and subject to erosion.

Sedimentation Pollution

Fine suspended particles cause turbidity in waterways. In other words, they make the water less transparent, blocking sunlight. The decreased light will impede the growth of aquatic plants, which provide essential habitat for many aquatic animals, including young fish. Another way sediment can be harmful is by smothering the gravel beds where fish lay their eggs. Gravel beds provide a perfect surface for trout or salmon eggs to be protected, while still allowing for oxygen to reach the growing embryo. When silt covers eggs, it prevents this oxygen transfer.

Aquatic invertebrates can suffer from damage to their fragile filtering systems, and if they are sessile (immobile) they can be buried by sediment. Fine particles can eventually be transported into coastal zones, where they affect marine invertebrates, fish, and coral.

Some Helpful Practices

  • Deploying silt fencing or straw bales around sites where the ground is disturbed.
  • Using soil erosion best practices around construction sites.
  • Protecting vegetation along stream banks. Replant shrubs and trees if needed.
  • Using cover crops on farmland when not actively growing regular crops.
  • Practicing no-till farming.
  • Follow best practices during forestry operations. This includes building appropriate stream crossings, avoiding operations in excessively muddy conditions, and selecting work equipment that will minimize damage to soils.


Unknown. "Voluntary Best Management Practices for Water Quality." 2018 Edition, New York State Department of Environmental Conservation, 2018, NY.

Castro, Janine and Frank Reckendorf. "Effects of Sediment on the Aquatic Environment." Working Paper No. 6, Oregon State University Department of Geosciences, August 1995, OR. 

Mid-America Regional Council. "What Is Sediment Pollution?" EPA, Kansas City, MO.