The surprising fact may be that 90% of the streams studied by the USGS had in some way been altered. Some of the causes for alteration may include "reservoirs, diversions, subsurface tile drains, groundwater withdrawals, wastewater inputs, and impervious surfaces, such as parking lots, sidewalks and roads." (USGS Release) Water quality and the health of the ecosystem are also being negatively affected by some of these changes to the streams. As water managers get a better understanding of the ecological effects of altering stream flow, they will be able to make more informed choices about dealing with streams in a healthy way. For further details and information, see the aforementioned USGS releases.
Photo courtesy of Punit Prakash.