United States Office of Office of
Environmental " Research and Water
Protection Agency Development
EPA/822/F-97/006 April 1997
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Decreases in river flow have reduced
the channel width of the river and
formed sand bars. Elevated water
temperature, excessive nutrients and
low flows promote the growth of aquatic
weeds and algae that reduce water
qualify and disrupt the habitat of
cold-water fish and invertebrate species.
What is an ecological risk assessment?
n ecological risk'assessment evaluates the potential
adverse effects of human activities on the plants
land animals that make up ecosystems. The risk
assessment process provides a way to develop, organize
and present scientific information so that it is relevant
to environmental decisions. When conducted for a par-
ticular place such as a watershed, the ecological risk
assessment process can be used to identify vulnerable
and valued resources, prioritize data collection activities,
and link human activities with their potential effects.
Risk assessments provide a focal point for cooperation
among local communities and state and federal govern-
ment agencies, and provide a basis for comparing
different management options.
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(Falls
Why is tlie R/Hd-Snake River special?
Shis case study covers the middle reach of the
Snake Elver which runs about 100 kilometers
_ (62 miles) from Milner Dam to King Hill. The
watershed includes 22,326 square kilometers (8600
square miles) of land. The Snake River has long
been valued as a source of water for irrigation and for
generating hydroelectric power. Prior to impoundment
of the river approximately 24 native fish species were
found below Shoshone Falls, including chinook salmon,
Pacific lamprey, steelhead trout and white sturgeon.
This exceptional stream is threatened by
many stressors from the day-to-day activities of peo-
ple within the watershed. Dams and other diversion
structures, and land use practices in the watershed
have reduced flow rates allowing aquatic weeds and
algae to choke the river. The native
fish and invertebrates that require
cold, swiftly flowing water have been
lost or severely reduced in number.
Currently eight invertebrate species
are classified as either endangered or
threatened.
The middle
reaches of the
Snake River
lie in the
west-central
Snake River
Plain of
' "southern Idaho.
'Changes in flowcaused"by'dams~dnd irrigation withdrawal fragment
the river system and alter available habitat. Local land users, power
generators, and watershed mangers can work together to protect the
Mid-Snake River from the effects of flow alterations while maintaining
economic iLse of the river.
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How casn this valuable resource
be protected?
I his ecological risk assess-
ment' will analyze the
stressors and resulting
ecological effects in the
Mid-Snake Elver watershed.
The assessment promotes
community awareness of
ecological problems in the
watershed and will provide
information to resource man-
agers, including government
officials, organizations and the
public. These actions promote
environmentally beneficial
results.
Decreased water flow and
velocity permit the growth
of aquatic nuisance plant
species. Cold-water fish
species, including trout and
sturgeon, lose critical habitat
for spawning and their food
base in these environments.
How is ithe ecological risk
assessment being done?
Interested organizations
collectively developed a
management goal and a
scientific study approach. The
ecological risk assessment brought together numerous
organizations to develop a goal to maintain and restore
conditions that support the native cold-water biota of the
Mid-Snake River, while also maintaining the river's eco-
nomic value. The ecological risk assessment uses a water
quality model and field studies to analyze the impact of
stressors on the watershed. Water quality will be exam-
ined to determine relationships between land and water
use within the watershed and what effects are seen in
the river. By evaluating current and past conditions,
forecasts can be made about future risks associated with
land and water use decisions. A report describing the
management goals for the Mid-Snake River watershed
and the analysis plan for the assessment will be available
upon completion of the analysis described above. .... .
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How will the results
be used?
ihe Mid-Snake River
Ecological Risk
Assessment will
help resource managers
predict how potential
changes in land use and
river flow will affect the
biological communities in
the watershed. This will
enable resource man-
agers to make decisions
based on more informa-
tion. This project is
co-sponsored by the
USEPA's Office of Water
Sediment loading from human
activity, such as the visible plume
being released from this fish hatch-
ery, have direct ecological effects on
the riverine community. The sedi-
ment chokes the stream, narrowing
the channel and forming sand bars
that reduce the flow of water.
Sediment deposition makes the
riverbed unsuitable for indigenous
invertebrate and fish populations.
and Office of Research
'&= and Development as an effort to bring the science of
ra) risk assessment into the local community decision-
^ making process.
The U.S. Environmental Protection Agency thanks the following
for their participation in this case study:
Idaho Department of Health and Welfare — -—•-— • -
University of California at Irvine
Mid-Snake River Planning Group
University of Idaho
US Fish and Wildlife Service
Idaho State University
For more information, please contact
Patricia Cirone
US EPA Region X, MS-OEA-095
Risk Evaluation Unit
1200 Sixth Avenue
Seattle, WA 98101
(206) 553-1597
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