Loops are ubiquitous in animate and inanimate transport networks, from leaf venation to river deltas. Yet, current physical models fail to reproduce them accurately. We report a way of loop formation that manifests in remarkably diverse processes—from unstable fluid flows to the canal system of jellyfish. Near the breakthrough, when one of the branches reaches the outlet of the system, shorter branches revive and accelerate toward the longest one, ultimately leading to a reconnection event. This results in a hierarchical structure of interconnected fingers. Our explanation of the shared underlying mechanism behind the phenomenon significantly advances the understanding of how looping transport networks dynamically emerge.