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<br />, <br /> <br />the Colorado River basin now is an infrequent, though occasionally still spectacular. event. <br />The dams transform the river, in many segments, into a series of lakes, As the sediment- <br />loaded water backs up behind a dam, the sediments tend to drop out. While the surface area <br />.. of the reservoir is exposed to the sun, the underlying waters are not. Thus water released <br />from the reservoirs, drawn from this lower level, tends to be considerably clearer and colder <br />than native river flows. Moreover, dams create insurmountable barriers to migration, <br />effectively segmenting the river and potentially closing off access to spawning and rearing <br />areas. Colorado River dams have created highly desirable trout habitat, and large numbers of <br />introduced species of trout and other fish now reside in the river. Good habitat for trout, <br />however, is not goOd habitat for fishes native to the river such as the Colorado squawfish _ a <br />fact underlined by the precipitous decline of these species since water development began <br />during this century. <br />The Colorado squawfish was listed as an endangered species in 1967. Despite more <br />than 25 years of study since that time, the biological requirements for recovery of the <br />squawfish still are not fully understood. What is known is that the squawfish has entirely <br />disappeared from the lower Colorado River basin, occurring now only upstream of Glen <br />Canyon Dam.47 Spawning occurs between July and September and appears to be closely <br />linked to water temperature (which must reach or exceed 20 degrees C.). Eggs are deposited <br />in coarse cobble beds that must be relatively free of sediments. Hatching and survival of the <br />larvae are most successful under conditions where the water temperatures are even warmer. <br />Upon hatching, the larvae apparently drift downstream, seeking backwater areas out of the <br />river's current. In the fall and winter, the squawfish search out pools and other deepwater <br />areas. Colorado Squawfish can migrate considerable distances - in one case, a documented <br />distance of nearly 200 river miles between April and September. <br />In 1973, Congress passed the Endangered Species Act which, among other things, <br />directed the Secretary of the Interior to develop and implement "recovery" plans for listed <br /> <br />" This discussion is taken largely from the Biological Opinion for the Muddy Creek Reservoir Project, Graild <br />County, Colorado, Feb. 7, 1990, U.S. Fish and Wildlife Service. <br /> <br />21 <br />