Worldwide freshwater systems are impacted by climate warming and anthropogenic forcing, influencing water level and runoff regimes via changes in precipitation and landuse patterns. Especially for river-connected lake systems these rapid changes might have far reaching consequences where inland nutrient loading might accumulate along the river system and finally lead to destabilization of distant ecosystems like estuaries. Thereby lakes, through their influence on flow regime, might play a critical role in how much and how far local eutrophication events will be transported along the river network. Currently, studies on river-connected lake systems are scarce and largely based on data with both low temporal and spatial resolution. Furthermore existing meta-ecosystem theory rarely takes lake-to-lake connectivity into account. In this study, we modeled how local nutrient input influences phytoplankton and how both propagate along strong or weak connected lakes. These theoretical investigations were accompanied by an extensive field study on lakes located along the Upper Havel-river system in Northern Germany including shallow and deep lakes and covering various flow regimes. We investigated effects of local nutrient loading on regional-scale plankton development along river-connected lake chains. To achieve high temporal and spatial resolution, we measured water constituents combining automated in-situ probes with ground-based, space- and airborne reflectance measurements. The field data show that upstream nutrient input drove phytoplankton development along the entire lake chain due to tight hydrological linkage. Our results suggest that similar point sources can result in profoundly different maximum intensity, spatial range and regional-scale magnitude of eutrophication impacts in lake chains dependent on flow regime and lake characteristics. We highlight the potential of combining in-situ measurements with remote sensing to improve lake meta-ecosystems monitoring.