5001

• UCREFRP Catalog Number: 5001
• Author: Nicola, S. J.
• Title: Fisheries Problems Associated With the Development of the Lower Colorado River.
• USFW Year: 1981.
• USFW - Doc Type: \
• Copyright Material: YES

• •
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The success of the fish populations, and consequently, the amount of
angling they can support, is directly dependent on the quality of the
habitat of the lower river. As long as cold water is discharged from
lakes Mead and Mohave and as long as there is a hatchery nearby, good trout
fishing will probably remain available. The warmwater species, however, ~-
must maintain themselves by natural reproduction. There is no way of
knowing what the exact status of the warmwater fishes was in the period
following construction of the dams, but it is almost certain that game
fish production has been affected by dredging and channelization activities
(Beland 1953). And, faced with the prospect that demands for water from
the Colorado will increase, we can expect that the production of game
species will continue to be affected by these and other water management
practices.
It would be instructive at this point to review the status of dredging and
channelization on the lower river. Lake Mohave backs up through narrow
canyons essentially to the base of Hoover Dam. No channelization or dredging
has been undertaken here. However, the entire river between Davis Dam and
the town of Topock was dredged and channelized between 1949 and 1960.
Between Topock and. Lake Havasu the river flows through Topock Gorge and Topock
Marsh, an area of natural backwaters and marshlands that has been set aside
as a National Wildlife Refuge. The .Bureau began to channelize the river
below Topock in 1967, but public protests brought a halt to these activities
after only 2..5 km of river had been altered. Below Lake Havasu there is a
small irrigation diversion known as Headgate Rock Dam. A 37 km section of
river below Headgate Rock Dam was dredged and channelized in 1967. The
Bureau has plans to extend these activities for another 34 km to the Palo
Verde Diversion Dam, but, implementation of these plans has thus far been
successfully resisted by State and federal wildlife management agencies.
For the next. 77 km below the Palo Verde Diversion Dam, in what the Bureau
has designated the Palo Verde and Cibola diversions, extensive dredging and
channel modification was conducted from 1966-1970. In one section of the
Cibola Diversion the natural channel of the river has been completely
bypassed and the river now flows through an artificial channel 21 lmt long.
The velocity of the water in the channel is so great that effective fishing
is nearly impossible..
To complicate matters further, the Bureau mistakenly dredged deeper than
planned in the Cibola Diversion and now the river is "naturally" scouring away
the streambed in the undredged section below. Slowly but surely this "natural"
dredging is lowering the water table in the adjacent flood plain and one by
one the backwater lakes and marshes are drying up. If this process continues
unchecked it may eventually eliminate the last remaining 70 km of undisturbed
habitat in this section of the river, part of which is now included within
the boundaries of Imperial National Wildlife Refuge.
At present, of the entire 584 km of river below Lake Mead, only 128 km remains
as essentially unmodified flood plain habitat.