Biological invasions, such as commonly observed in dendritic riverine networks can change biodiversity, leading to global species loss and consequently alter ecosystem functioning. Key invariant regional scale properties such as habitat size, connectivity and dispersal properties, have recently been identified as drivers of community structures in river ecosystems. Those network properties are thus likely important to understand the success of invading species. Using protist microcosm experiments, I disentangled how patch size and patch connectivity affect the establishment success of invading species in dendritic river-like networks. I showed that invasion success and invader densities depend on the invading species and community composition. Further, I showed that a larger patch size as well as a high biodiversity in a patch immediately preceding an invasion reduced invasion success. Even more, the effect of diversity on invasion success changed across an increasing patch size gradient from a negative to a positive correlation, while overall increasing patch size reduced invasion success. Contrarily, connectivity did not have a direct effect on invasion success but indirectly affected invasions by shaping diversity patterns in the whole network. My results emphasize that it is essential to manage invasions of species on a landscape level to protect vulnerable ecosystems.