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Providing passage would also benefit Colorado squawfish by extending their range and allowing them access to additional flooded bottomland habitat. Habitat Enhancement Historically, upper Colorado River basin floodplains were frequently inundated by flows during spring runoff, but today floodplains are not regularly connected to the river because of channelization by levees, dikes, or rip-rap near population centers and in agricultural areas. The frequency of out-of-channel flooding in the upper Colorado River has dramatically decreased following the onset of transmountain water diversions, irrigation diversions, and the construction of mainstem dams for storage (Osmundson and Kaeding 1991). The construction of dikes coupled with the reduction of high spring flows has altered the natural hydrograph and either reduced or eliminated regular flooding of bottomlands. Numerous studies (Grawboski and Hiebert 1989; Maybe 1993; Tyus and Karp 1989; Wydoski and Wick 1994) have suggested the importance of seasonal flooding to river productivity. Protection, restoration, and enhancement of flooded bottomland habitat is thought to be particularly important for recovery of razorback sucker because when available it is believed they use them extensively for feeding and nursery areas and possibly even as spawning areas. Restoration of wetland habitats adjacent to the river corridor that historically flooded but no longer become inundated during the late spring and early summer may be an important factor in the re-establishment of self-sustaining razorback sucker populations in previously occupied river reaches. Larval razorback sucker may need access to productive wetland habitats during the late spring period when they are drifting downstream immediately following spawning. Habitat enhancement may provide the means by which bottomlands, presently cut-off from the mainstem river, could be inundated during early spring and summer and provide productive nursery and feeding areas for razorback sucker larvae. These productive off-channel areas are also thought to be important staging and resting areas for adult razorback sucker in the spring prior to spawning. Providing this access may be very critical to the ultimate recovery of the razorback sucker. Irving and Burdick (1995) identified bottomland habitat sites both immediately downstream and upstream of Hartland Diversion Dam. Restoring bottomland habitat upstream of Hartland Diversion Dam will provide an additional six sites totaling 375 acres for use by razorback sucker, which will assist in re-establishment of razorback sucker in the Gunnison River. The merits of providing fish passage at Hartland Diversion Dam include, 1. Extending the upstream range and re-establishing native endangered Colorado squawfish, and razorback sucker to previously occupied reaches of the Gunnison River, 2. Increasing the potential number of bottomland sites and opportunities for habitat restoration and enhancement to assist recovery of endangered fishes, particularly 5