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As alternate reservoir-controlled hydrographs are tested and evaluated, the multiple year effects will consider other impacts of the biological response and statistical significance before reaching conclusions on the desirability of any particular flow regime. Secondary Channel Ichthyofaunal Characterization - Fish communities of secondary channels of the San Juan River between Hogback Diversion, New Mexico and Bluff, Utah were inventoried during summer lowflows in 1991 and spring runoff and summer lowflows in 1992. Four types of secondary channel (based upon length and proportion of total stream discharge) and 21 macrohabitat types (defined by water velocity, depth, substrate, location in relation to channel bank, and cover type) were recognized. During summer lowflows, fish populations were sampled by macrohabitat type while sampling was by secondary channel for most spring runoff collections; several small secondary channels were sampled by macrohabitat. Non-native red shiner was the most abundant species found in secondary channels during summer lowflows in both years. Also moderately common were non-native fathead minnow and native speckled dace and flannelmouth sucker. During 1991 and 1992 spring runoff, however, native flannelmouth sucker, speckled dace, and bluehead sucker were the most abundant species found in secondary channels. Non-native red shiner and channel catfish were moderately common. No rare fishes (roundtail chub, Colorado squawfish, or razorback sucker were found in secondary channels during this phase of the study in 1991 or 1992. Common carp, bluehead sucker, and channel catfish were moderately common in secondary channels during spring runoff, but were very rare in secondary channels during summer lowflows. Plains killifish was irregularly collected in secondary channels during summer lowflows but was not found in them during spring runoff. Relative abundance of several species varied longitudinally in one or both seasons in 1992. Bluehead sucker was found in most secondary channels during spring runoff, but was absent from secondary channels downstream of River Mile 135 during summer lowflow. Flannelmouth sucker had a similar pattern of declining abundance in downstream secondary channels during summer lowflows. No other commonly collected species exhibited as distinct longitudinal abundance patterns, but differences were discerned. During summer lowflows, some segregation of species by macrohabitat type was noted. Red shiner and fathead minnow were more-common in low-velocity macrohabitats. Although comparatively common in low- velocity macrohabitats, flannelmouth sucker tended to be more common in intermediate-velocity macrohabitats. Speckled dace was most common in intermediate- to rapid-velocity macrohabitats. 17