We placed Rainbow Trout Oncorhynchus mykiss or Westslope Cutthroat Trout Oncorhynchus clarki lewisi in the outlet pool of an open-channel flume in Bozeman, Montana, USA, in 2011 and allowed fish to enter and traverse the flume volitionally. We used video cameras to track fish trajectory against an observed combination of water flow depth and velocity. In each trial, we introduced fish of one species and within a size class to the flume in a batch. The conditions and participants in each experimental trial are summarized. The abbreviation std dev is the standard deviation of the mean water velocity.