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81 Some artificially-protected areas were noted at Station Y-1 behind large concrete slabs. The radical channel alterations constructed in 1976 at this station produced a segment similar to that at Y-2, with a "raceway" of low habitat diversity adjoining a sluggish backwater. Again, the probability of loss of reproductive isolation, by removal of original spawning habitat, was high. Habitat reduction at Stations Y-1 and Y-2 does not explain the abundance of white X flannelmouth and white X bluehead sucker hybrids compared to hybrids between the flannelmouth and bluehead suckers. If all suckers were induced to spawn in the crowded backwater reaches at the same time, similar proportions of the three hybrid types would be expected. Low proportions of bluehead X flannel- mouth hybrids even under stress conditions indicate mainte- nance of the temporal reproductive isolation usually attributed to sympatric fishes which evolved together in an area isolated from outside biotic influences. The relative abundance of white X flannelmouth sucker hybrids at Station Y-3 was influenced by capture of several such fish on one sampling date. Hybrids were not common at Station Y-3 on other dates. White X flannelmouth hybrid occurrence reflects abundance at Station Y-3 of the latter parent but is not consistent with the relative scarcity of the other parent. River conditions at Station Y-3 were con- sidered relatively unchanged by channelization, and spawning areas were numerous. It is likely that such hybrids were