The Szigetköz braided branch system was once among the most important spawning areas for migratory fish in the Danube. Extensive river engineering, most notably the construction of the Gabčíkovo barrage, has since caused severe ecological degradation and fragmentation of the river corridor. In response, the SWIM project aims to map migratory routes and critical habitats, evaluate the functionality of fish passes, and support the long-term restoration of the Danube’s ecological connectivity.

A key objective of the Hungarian pilot is to study sterlet (Acipenser ruthenus) migration and identify its most important habitats in the Szigetköz region. However, recent scientific results obtained after the original proposal was submitted show that sterlet occur only rarely in the initially planned pilot area (the 45-km stretch between Dunakiliti and Gönyű and the lower Moson Danube). Slovak telemetry data indicate that a significant proportion of sterlet tagged at the Gabčíkovo hydropower plant migrate downstream toward the Danube section upstream of Budapest. To ensure effective monitoring, the Hungarian pilot area has therefore been extended to the Nagymaros–Budapest section, where sterlet are more abundant and better suited for telemetry studies. This adjustment enables the Hungarian monitoring to complement the Slovak system while maintaining full technical compatibility and systematic data exchange.

The revised pilot design continues to support SWIM’s original goals: mapping fish migration routes, identifying key habitats, particularly for sterlet, assessing fish pass effectiveness, and contributing to the restoration of the Danube’s ecological corridor through coordinated, cross-border research.