WSP06185

• File Number: 8220.101.09B
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 1/1/1994
• Title: Comments re: Operation of Glen Canyon Dam Draft Environmental Impact Statement
• Water Supply Pro - Doc Type: EIS

* Water level fluctuations of more than 30 feet during the
course of a year dictated vegetation distribution and density.

* Little canopy developed in the Old High Water Zone above
the scour zone. Forms consisted of desert stream forms like
the hackberry, mesquite, and acacia.

* Riparian species of wildlife were limi ted since the
riparian habitat was limited.

* Peregrine falcons and Bald eagles were likely rare due to
the lack of a reliable food supply.

* Wintering waterfowl concentrations did not occur prior to
dam construction.

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* Continuous muddy condition limiting light penetration to
the river maintained rather meager primary (algae) production.
This limited secondary production which affected both numbers
and kinds of fish and riparian wildlife.

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* Fish species were typical warm water species consisting of
mostly nonnative fish which had come to dominate the native
fauna by the time dam construction commenced.

* Prior to dam construction, nonnative catfish and carp
predators dominated the fish community, comprising about 80
percent of all fish present. This change in dominance to
nonnatives developed despite the presence of temperature, flow
and sediment conditions which supposedly favors native fish.

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* Trout populations and sport fishing for trout was non-
existent due to the warm, muddy conditions.

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* Recreation use of the river was limited due to instability
of flows and the likelihood for extreme changes in flow.

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Pre-dam conditions were characterized by a harsh environment of
extreme flow events, extremes in temperature and high turbidity.
These conditions were probably responsible for the low diversity of
wildlife and plants. Although the terrestrial habitat was
virtually pristine and, on the surface, the river seemed natural,
the fish life had changed dramatically and forever by colonization
by nonnative fish. The Bureau of Reclamation should ask those
entities most concerned about maintaining a natural system through
changes to facilities and operations if this means return to pre-
dam conditions described above.

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