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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