NOTE Measurement structures and fishpasses have inherently different hydraulic performance criteria. Water measurement structures perform better with uniform flow patterns; conversely, fish passage performance is improved by the variability of the flow conditions that allow fish and other aquatic inhabitants to select the passage conditions that best meet their mode of movement. This International Standard does not suggest that the fishpasses discussed are the preferred methods of passage or that they are good enough that passage performance can be sacrificed to obtain a single structure that does both.