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. . ('"\ :.~ ~"i~'" pressure on the reservoirs coupled with the lack of sufficient spawning areas, an estimated 72.9 tons of hatchery reared fish will be required annually to stock Project reser- voirs. There may be additional species stocked in the res- ervoirs, as has occurred in completed facilities; this stocking includes species that did not, or could not, inhabit the streams. Such species include lake trout, the Bonneville cisco, kokanee salmon, and smelt in the cold water reservoirs. Trout will .be.stocked in Pueblo Reservoir; however, trout had been observed in the Arkansas River prior to the impoundment of the water. Due to the need for addi- tional fish, the Bureau will provide 6.7 second-feet of water to the hatchery at Leadville. There will also be a warm water hatchery and cold water rearing unit at Pueblo Reservoir. These facilities will provide fish for Project reservoirs and increase the fish production in the State. The most significant change in species composition as a result of the impoundment will occur in the plankton and benthos. The organisms in the lotic communities differ significantly from lacustrine communities. The naiads (aquatic nymphs) that abound in the riffle aress of pro- duction streams are restricted to the littoral zone of reservoirs, However, in fluctuating reservoirs, benthic production and organisms are limited. Aquatic insect larvae in lakes are more commonly of the order Diptera, e,g. bloodworms, and Tricoptera, rather than the Plecoptera (stoneflies), Odonata (dragonflies), and Ephemeroptera (mayflies). The benthos then undergoes a nearly complete change in species composition although the Tricoptera (caddiflies) are common in both lakes and streams. . . Algae also differ significsntly between the two types of habitat. In a stream the algae are restricted to those. that can become attached to a substrate, such as rocks and rooted aquatic plants. All others are washed downstream. There are also attached algal species (periphyton) in lakes. However, these are a minor contributor to the total primary production of the lake. Since most of the lake is open water area, planktonic species account for most of the primary production and its contributing biomass. Some of these individuals pass through the dam and can enter the downstream ecosystem, but only on a temporary basis. Fish inhabiting a reservoir following inundation of their former stream habitat mUSL change their diet. Species that can subsist on a wide range of forage, such as rainbow trout, do well in these circumstances. However, other less desir- able species may become competitive fOllowing impoundment. . IV-35