The Atlantic blue crab, Callinectes sapidus, is among the fastest-expanding invasive species in the Mediterranean Sea, where it has established dense populations in coastal and estuarine habitats. Although its ecological impacts in these environments are documented, its occurrence and role in inland freshwater ecosystems remain poorly understood. A previous study conducted along the Po River (Italy) between 2022 and 2025 demonstrated that this species can migrate more than 160 km upstream. The present study investigated whether the restoration of freshwater connectivity through fish passages may facilitate the dispersal of non-native species such as the blue crab. During spring 2026, three fish passages located along branches of the Po River were monitored: Valle Lepri (14 km from the coastline), Tieni (23.5 km), and Valpagliaro (45 km). A total of 115 blue crabs were captured: 42 individuals were recorded at Valle Lepri and 73 at Tieni, no crabs were detected at Valpagliaro. The population was strongly composed by males, with 95% of captures at Valle Lepri and 98% at Tieni. The mean size of individuals at Valle Lepri was 6.3 cm and 29.4 g, while crabs collected at Tieni had a mean size of 12.9 cm and 38.5 g. These values are considerably lower than those recorded in the Goro Lagoon during the same period (16 cm and 120 g on average), suggesting that intraspecific competition within established populations may promote upstream dispersal. In particular, smaller and younger individuals may be more likely to colonize new available habitats. These findings highlight a potential trade-off in river restoration: although fish passages are essential for restoring connectivity and supporting threatened migratory species, such as the European eel, they may also facilitate the spread of invasive alien species. Further monitoring is needed to assess the ecological consequences of blue crab colonization in freshwater ecosystems.