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RESTON, VA. — The amount of water flowing in streams and rivers has been significantly altered in nearly 90 percent of waters that were assessed in a new nationwide U.S. Geological Survey (USGS) study. Flow alterations are a primary contributor to degraded river ecosystems and loss of native species.

Flows are altered by a variety of land- and water-management activities, including reservoirs, diversions, subsurface tile drains, groundwater withdrawals, wastewater inputs, and impervious surfaces, such as parking lots, sidewalks, and roads.

“Altered river flows lead to the loss of native fish and invertebrate species whose survival and reproduction are tightly linked to specific flow conditions,” said Daren Carlisle, USGS ecologist and lead scientist on this study. “These consequences can also affect water quality, recreational opportunities, and the maintenance of sport fish populations.”

Overall, the USGS study indicated that streams with diminished flow contained aquatic communities that prefer slow-moving currents more characteristic of lake or pond habitats.

The study identified more than 1,000 unimpaired streams to use as reference points to create stream flow models. The models were applied to estimate expected flows for 2,888 additional streams where the USGS had flow monitoring gauges from 1980-2007. The estimated values for the 2,888 streams were compared with measured flows to determine the degree to which streams have been altered.

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