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643 of the three categories of spring flows (> I 0,000 cfs, >8,000 cfs, >5,000 cfs). Under the proposed plan, 644 the desired frequency and duration of the categories are fully met or exceeded. Because of this, the 645 spring flows under the proposed action should meet many of the purposes of the flow 646 recommendations, including generation of new cobble sources, creation of channel diversity,provision 647 of nutrient loading, maintenance of spawning areas, and creation and maintenance of backwaters and 648 other low-velocity habitats. 649 Maintaining low. stable base flows enhances nursery habitat conditions and flows between 500 and 650 1,000 cfs optimize backwater conditions-selecting flows at the low end of the range increases the 651 availability of water for development and spring releases. Bliesner and Lamarra (2000) reported that 652 backwater habitats, which are extremely important for the endangered fish, demonstrated a high degree 653 of variability at low flows; but low flows clearly maximized this habitat Juvenile low velocity habitat 654 is likely maximized between 800 and 1,000 cfs (Service, 200Id). 655 The proposed plan includes operations to attempt to maintain the base flows in the 500 to 1,000 cfs 656 range; however, this cannot always be accomplished. Inflows from tributaries, combined with even 657 minimum releases from Navajo Dam, will cause the 1,000 cfs to be exceeded at times. This is 658 particularly true during spring runotfwhen downstream tributaries are high and during the frequent 659 summer thunderstorms that can add sudden spike flows to the river. In addition, there are difficulties 660 with travel time for changed releases to reach critical habitat and discrepancies with gage readings in 661 the critical habitat area. 662 Bliesner and Lamarra (2000) report on studies that relate flow levels to habitat creation and 663 maintenance and should be referred to for further information. 664 The proposed action will affect water quality in the San Juan River. Releases from Navajo Reservoir 665 of high quality water generally dilutes pollutants downstream. This dilution effect will be increased 666 during certain periods under the proposed plan but will be decreased in the winter months and 667 periodically at other times of the year as releases are reduced. Contaminants of concern include P AHs 668 and trace elements such as selenium, arsenic, copper, and zinc. Simpson (1999) concluded "...that the 669 concentrations of contaminants in biota inhabiting the main stem of the San Juan River were not 670 consistently correlated with instream flow discharges." 671 There is some belief that a more natural hydrograph may result in some natural control of non-native 672 fish that compete with the endangered fish. This hypothesis was studied and initial conclusions are 673 that a negative response of non-natives to the more natural hydrograph during the test flow period did 674 not occur (Brooks, et ai, 2000). 675 Overall, the proposed action should beneficially affect the Colorado pikeminnow and its designated 676 critical habitat; water quality changes associated with low flows may have adverse impacts under 677 certain conditions when dilution flows are reduced. The proposed action also provides for adaptive 678 management so that adjustments can be made to reflect new research and findings. 23 ; ,