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The Mesa County DeBeque gravel pit and the Colorado River Overflow are both located above the Government Highline Canal diversion structure, while the other sites are located below the structure. This is considered important because the diversion structure constitutes an effective fish barrier preventing upstream migration of the endangered fish. As a result, the fish populations above and below the Government Highline diversion have been essentially separate populations since construction of the diversion in the early 1900s. CDOW inventories between 1971 and 1973 of the Colorado River above the diversion indicated that no other significant spawning areas were present above the diversion. Mr. Kidd's observations indicated that razorback suckers tended to remain in the same general area of the river throughout their life cycle. If an area of the river provides all of the habitat requirements of the species, the individuals do not appear to move great distances. In many cases, the same fish were found in the same backwater areas year after year, moving out only when water depths became too shallow. 4.2 NATIVE FISH DISTRIBUTION Based on Mr. Kidd's observations, razorback suckers were relatively common in the Upper Colorado from the Utah state line to Rifle through 1975. The population appeared to be relatively stable based on the numbers of fish present, and the evidence of recruitment. Razorback suckers could be easily collected almost anywhere in the Colorado River up to Rifle. The Colorado River Overflow was recognized as an important spawning area in the DeBeque- Grand Valley Final Environmental Impact Statement (EIS) of 1975. This document describes the anticipated impacts of construction of Interstate 70 between Plateau Creek and Rifle. In addition, the CDOW, the U.S. Environmental Protection Agency ( EPA), and U.S. Interior Department commented on the importance of the Colorado River overflow in this document. During the preparation of this EIS, Mr. Kidd predicted that if the Colorado River Overflow was disturbed by construction of Interstate 70, the razorback sucker populations would be seriously impacted. By 1980, the Colorado River Overflow had ceased to function for razorback sucker spawning due to alterations related to the Interstate 70 project. Extensive riprapping of the shoreline apparently altered the flow characteristics of the area, resulting in rapid siltation and establishment of extensive stands of tamarisk shrublands. %27JaMRT9MAWPP-C.W WE 6