mil United States
Environmental Protection
Agency	December 2016
Fact Sheet— Final EPA-USGS Technical
Report: Protecting Aquatic Life from
Effects of Hydrologic Alteration
Summary
EPA and U.S. Geological Survey (USGS) have released
a report, Final EPA-USGS Technical Report:
Protecting Aquatic Life from Effects of Hydrologic
Alteration. This report presents:
•	a literature review of the natural flow system
and a description of the potential effects of flow
alteration on aquatic life;
•	examples of narrative water quality criteria that
some states have developed to support natural
flow and maintain healthy aquatic biota; and
•	a flexible framework that can be used by states,
tribes, and territories to quantify targets for flow
regime components that are protective of
aquatic life.
Background
EPA and USGS partnered in developing this technical
report on hydrologic alteration, which can be an
important contributor of impairment for water
bodies that are designated to support aquatic life.
Stresses on aquatic life associated with hydrologic
alteration may be further intensified through climate
change. Recent climate trends have included the
change in frequency and duration of extreme
weather events, such as droughts and floods, which
can have an impact on flow and affect aquatic life.
Technical Report Development
This document has undergone internal and external
peer reviews and was released in the Federal
Register for a 105-day public comment period. EPA
and USGS considered the comments, revised the
document, as appropriate, and then published a final
document to serve as a source of information for
states, tribes, territories, and other stakeholders.
Hydrologic Alteration
Hydrologic alteration is a change to an aquatic
system and can include an increase or decrease in
water volume, seasonal pulse flow disruption,
dramatic variation in water temperature, and other
factors.
Effects of Hydrologic Alteration
The ability of a water body to support aquatic life is
tied to the maintenance of key flow components.
Changes in the natural flow conditions can cause
some of the following effects:
•	Physical Changes: altered flood-plain
connectivity; and altered channel properties,
such as widening
•	Water Quality: increases in salinity,
sedimentation, and water temperature
fluctuations
•	Seasonal Flows: decrease in cues for species
spawning; can also encourage establishment
of non-native species

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Why this Report is Important
Healthy aquatic ecosystems provide an array of
services to individuals and society, including clean
drinking water, irrigation supplies, and recreational
opportunities. Sound and sustainable management
of aquatic ecosystems is an integral part of managing
water resources to meet the needs of society and
the goals of the Clean Water Act.
This report provides a scientific and technical
framework that can be used to quantify targets for
flow components that are protective of aquatic life
and their habitats. Flow targets can help states,
tribes, and territories prepare for changes in historic
flow patterns that can result from climate change.
Maintaining flow targets may help increase a
stream's resilience to climate change by reducing or
avoiding intensification of existing stresses.
How to View the Report and Supporting
Information
EPA has established an official public docket for this
action under Docket ID No. EPA-HQ-OW-2015-0335,
accessed at https://www.regulations.gov/. You may
also download the report and supporting
information from EPA's aquatic life criteria website
at: https://www.epa.gov/wqc/aquatic-life-ambient-
water-quality-criteria.
Where to Find More Information
For more information, please contact EPA's Diana
Eignor by phone at (202)566-1143 or by email at
eignor.diana@epa.gov; or contact USGS' Jonathan
Kennen by phone at (609)771-3948 or by email at
jgkennen@usgs.gov

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