Abstract: Fragmentation of river networks has been pointed out as one of the most serious threats to the sustainability of fish populations. Although far more numerous than dams, the impact of small weirs on fish movements have received much less attention. The presence of these barriers alters the water depth and velocity patterns and creates vertical drops that change the hydraulic environment, leading to connectivity losses with negative consequences to the persistence of fish communities. This study aims to evaluate the passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei) when encountering small weirs of varying heights associated with variable plunge pool depths. A factorial design consisting of 16 configurations (4 replicates each), was carried out in an experimental flume with schools of 5 fish for each test (mean total length = 18.7cm ± 3.3 cm) at a flow discharge of 50 L.s-1. Different combinations of plunge pool depths (z=10, 20, 30, and 50 cm) and heights of the jump (h=5, 10, 15, and 25 cm; distance from the plunge pool surface to the top of the weir crest) were tested. Both variables and their interaction term (z x h) were significantly correlated with the number of successful weir negotiations by fish (PerMANOVA, p< 0.01). The highest number of passages (n=50) occurred for a combination of z=20 cm h=10 cm, and the lowest (n=1) for a combination of z=10 cm h=25 cm. Results showed that increased passage does not necessarily occur at higher water depths in association with lower height of the jump. Thus, successful negotiation seems to be a more complex phenomenon where both variables interact to set the most effective hydraulic conditions for fish. These outcomes are useful to define design criteria for the requalification of small barriers to improve fish passage and habitat connectivity.