Laboratory studies suggest that fishes are capable of using fine-scale structures to avoid swimming. Similar structures occur as dips, ripples, and eroded areas behind protruding rocky materials, within the riffle-run-pool margin structure of streams. It is not known if loboratory-determined capabilities are used to avoid swimming in the field. I measured current speeds for in-stream structures from coarse-scale riffle-run-pool-margin to fine-scale substratum ripples and determined fish locations in these structural features during the day and night. During the day, most fishes were seen in pools, margins, and runs, which is consistent with indirect responses to predation. At night, fishes from runs and ripples moved to the lowest current speeds, including those provided by fine-scale structures in the bottom of runs and riffles with dimensions comparable to minima used in laboratory settings.