Stream ecology research in the mountains of El Yunque National Forest laid the foundation for understanding aquatic ecosystems in Puerto Rico. Cathy Pringle, through her work and collaborations on the island, applied her expertise on benthic algae to demonstrate the critical role of animal consumers (e.g., fish, shrimps) in regulating benthic resource levels and ecosystem processes. Building on this foundation, her research expanded beyond El Yunque to examine how hydrologic connectivity shapes stream ecosystems across the island. Large dams severely disrupt this connectivity, blocking migratory animals from reaching headwater streams and leading to their extirpation. Here, we present data from over 20 streams spanning more than a dozen watersheds across the island. Through in-situ experimental manipulations and extensive surveys, we demonstrated that these extirpations result in (a) higher levels of benthic algae, organic matter, and nutrients and (b) slower leaf litter breakdown in streams above large dams compared to free-flowing streams where the stream community remains intact. These landscape-scale changes in ecosystem properties and processes highlight the importance of maintaining connectivity between headwaters and the ocean to sustain consumer populations and ecosystem function.