Contrarily to the vast literature on dams, much less is known about the effects on fish movements of the far more numerous small weirs. This study aims to evaluate the negotiation performance of the Iberian barbel (Luciobarbus bocagei), a medium-sized potamodromous cyprinid, facing a small broad-crested experimental weir with varying widths of the weir crest (W), and discharges (Q). Hydrodynamics over the crest and downstream the weir were characterized with a flow probe and a 3D Acoustic Doppler Velocimeter. Fish negotiated all configurations W×Q tested, registering a total of 273 upstream passages and 192 downstream passages. However, the number of fish that approached, attempted, and successfully ascended and descended the weir varied among configurations, emphasizing the complex interaction of factors on passage performance. Discharge proved to be preponderant on both upstream (F = 5.48; P = 0.008) and downstream passage (F = 6.66; P = 0.009), while the influence of the width of the weir crest was more evident on downstream passages (F = 5.16; P = 0.016). Results from this study are expected to be useful to identify potential migration obstacles and may be applicable to other cyprinid species with similar life-history requirements.