Sediment is made up of loose particles of sand, silt and clay. It is a natural part of the Chesapeake Bay, created by the weathering of rocks and soil. But in excess amounts, sediment can cloud the waters of the Bay and its tributaries, harming underwater grasses, fish and shellfish.

There are two main sources of sediment to the Bay:

  • Watershed erosion from land and stream banks. Watershed erosion increases when land is cleared of vegetation to make way for agriculture and development. Scientists estimate that most of the sediment that flows into the Bay comes from watershed sources.
  • Tidal erosion from shorelines and nearshore areas. Tidal erosion increases when shoreline vegetation is removed and there are not enough grasses growing offshore to lower the force of waves against the shoreline.

Because of their small size, the particles of sand, silt and clay that we call “sediment” often float through the water rather than settling to the bottom, and can be carried long distances during rainstorms. When there are too many sediment particles suspended in the water, the water becomes cloudy and muddy-looking. Cloudy water does not allow sunlight to reach the plants that grow on the bottom of the Bay’s shallows. Without sunlight, these plants—like underwater grasses—die, which affects the young fish and shellfish that depend on them for shelter.

Excess sediment can also have harmful effects on the wider Bay and the people who use it:

  • Nutrients and toxic contaminants can bind with sediment, spreading through the Bay and its waterways. Fish and shellfish that live and feed on or near contaminated sediment can become contaminated themselves, triggering fish consumption advisories.
  • Excess sediment can smother oysters and other bottom-dwelling species.
  • Accumulating sediment can clog ports and channels, affecting commercial shipping and recreational boating.