Human–environment interactions relating to changes in the hydrological system of the Upper Vistula valley are poorly understood. This valley lies in the foreland of the Transcarpathian transition, an area in Central Europe, which is crucial for the migration of people. Using palaeobotanical and geochemical analyses, archaeological data, and data on the river's fluvial activity, we retrace the sequence of environmental changes occurring in the vicinity of the bog in Strumień during the transition between the Iron Age and the Early Middle Ages. The stability of changes in the river valley under the influence of human activity is also assessed. It is shown that:
There was variation in human pressure on the environment in the Iron Age and the Middle Ages. Following a decline during the Migration Period, it increased again in the Early Middle Ages.
The use of floodplains, including for pastoralism and cereal growing, was dependent on the changing hydrological conditions.
During the Migration Period and in the Early Middle Ages, changes in the climate and related hydrological conditions were key factors influencing changes in hygrophilous riparian ecosystems. Human‐induced changes in these ecosystems were reversible.