Skip to main content

Approximately 41,204 miles of streams in Minnesota (49.6% of the total) have been altered in some way by humans. Channelizing, ditching, and damming projects have changed the natural course of streams and their drainage areas. Altered stream channels can result in higher flows, higher levels of pollutants entering waterways, and degraded habitat. They can also make the environment less resilient to extreme weather.

In the past streams and rivers were altered to:

  • increase agriculture capacity.
  • increase land value.
  • improve highway and railway transportation.
  • remove swamps and wetlands (mistakenly thought of as “disease-breeding areas”).

The MPCA worked with the Minnesota Geospatial Information Office to create a statewide inventory of streams that have been hydrologically modified (e.g., channelized, ditched, or impounded). Project staff reviewed approximately 105,000 miles of streams to classify them into four major categories:

  • Natural
  • Altered
  • Impounded – Waterways with dams or other barriers that impound water upstream
  • No definable channel – Include swales through agricultural fields; shallow, wide, grass waterways; some wetland and lakes; and streams that disappeared or are now subterranean, usually in urban areas

The map below indicates stream channels that were designated as altered, natural, and impounded.