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I I ,Ii I I I I I I I' II i I I j I I I .1 The reduction in the annual flood peak also permitted the establishment of marshes in some low, sandy areas along the riverbanks. The increase in area of vegetation along the river, and the addition of new habitats such as marshes, riparian trees, and dense shoreline vegetation, allowed an increase in population densities of a number of wildlife species, including the rare bell's vireo and willow flycatcher. Also, many birds that did not nest along the river before 1963, now do. (See Appendix B, Sections II and IV.) Fish. The change from warm, sediment-laden water to cool, clear water has changed the aquatic food base in the river, greatly increasing the supply of algae and associated invertebrates. Trout can now exist in the river due to the lower temperature and sediment concentrations, and thrive on the new food base. However, the cold water has been detrimental to the warm-water native fish. Of eight native species originally found in Grand Canyon, only four remain in significant numbers. The spawning area for one of these, the humpback chub, is now limited to the Little Col~rado River. (See Appendix B, sections II and IV.) Recreation. Recreation in Glen and Grand Canyons has greatly increased since completion of the dam in 1963. Today, fishing for trout in Glen Canyon, made possible by the cold water released from the dam, is a major recreational activity generating approximately $0.5 million in recreation benefits annually. White-water rafting has grown from fewer than 200 boaters in 1960 to about 16,000 in 1972. Today, white-water boating generates approximately $4 to $9 million in recreation benefits annually, depending upon flow conditions. Although regulation of river flows and the resulting lengthening of the white-water season has certainly been a factor in this increase, white-water boating has increased dramatically in popularity nationwide during the same period. Other rivers in the United states, both controlled and un- controlled, have experienced dramatic increases in white-water boating in the last 10 to 20 years. This suggests that white-water boating use of the Colorado through the Grand Canyon would be very high without Glen Canyon Dam, but probably not as high as with flow regulation (Appendix C, Section I). 30