Over time, sediments (soil, rock, etc.) ever so slowly finds its way into a stream or other waterway. The natural forces of erosion, though, occur in a way that still protects aquatic health in local waterways. Through various practices of man, sediment finds its way into our streams more easily and more often.
Development processes can cause significant soil erosion that can escape from a development site and find its way in local creeks and ponds.
Other extraction-based industries, like surface coal mining, fundamentally modify the structure of the earth and expose minerals and sediments in massive quantities to erosive forces with wind and rain. This can result in the transport of these sediments off-site, even with various practices intended to prevent such an occurrence.
Finally, farming, if done without using sound practices, represents a very significant potential source of sediment into local waterways.
With all these issues, we work to try and reduce potential problems. Most of these are dealt with through various other Clean Water Policy programs, like the Farm Bill work, or the monitoring of and commenting on applications for 401, 404, and/or 402 permits.