WSP04316

• File Number: 8220.105.I
• Description: Colorado River-Water Projects-Navajo-Environmental Studies
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/2002
• Author: BOR
• Title: Navajo Dam EIS-Biological Assessment-Advanced Draft
• Water Supply Pro - Doc Type: EIS

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BIOLOGICAL ASSESSMENT-

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INTRODUCTION

This Biological Assessment is prepared pursuant to Section 7 of the Endangered Species Act of
1973 (ESA), as amended, to address impacts of operating Navajo Dam and Reservoir on
threatened or endangered species, species that are candidates for listing, and other species of
concern.

Navajo Dam was constructed between 1958 and 1963 under the Colorado River Storage Project
Act of 1956 to meet multiple water resource purposes. The dam is located on the San Juan River
approximately 44 miles upstream from Farmington, New Mexico. The reservoir created holds
approximately 1.7 million acre-feet of water and extends into both New Mexico and Colorado.

In addition to regulating river flows, the reservoir stores water tor the Navajo Indian Irrigation
Project (NIIP) and various municipal and industrial uses. At the present time, NIIP diverts an
average of approximately 160,000 acre-feet (at) from the reservoir for irrigation south of
Farmington. In the future this use is expected to approximately double. The storage and release
of water for downstream uses allows upstream diversions to be made for the San Juan-Chama
Project. Navajo Dam provides flood control and also recreation and fishery benefits. The
reservoir has a surface area of 15,610 acres and has 150 miles of shoreline. The nonnal
operating range for the reservoir is between 5,990 feet and 6,085 feet. Navajo Reservoir has a
maximum content of 1,701,300 af. Below 5,990 feet is the inactive pool containing 625,675 af
of water.

Reclamation requested initiation of Section 7 consultation on the operation of Navajo Dam in a
memorandum to the Fish and Wildlife Service (Service) dated July 30, 1991. The Service
(1991) concurred with a request from Reclamation that consultation on the operation of Navajo
Dam and Reservoir under Section 7 of the ESA be extended while research was conducted on
flow needs of endangered fish in the San Juan River. During the research period, which
extended from 1991 to 1997, Reclamation provided test flows to mimic a natural hydrograph.
Following the research period, a report on flow recommendations for endangered fish was
prepared (Holden, 1999).

The Service and Reclamation have consulted fonnallyand infonnally throughout the 1990's
regarding the potential impacts of operation of Navajo Dam on listed species. Reclamation plans
to implement the proposed action-to operate Navajo Dam to meet flow recommendations for

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