In the 1980’s, Dr. Cathy Pringle discovered that some streams at La Selva Biological Station, Costa Rica, are fed by solute rich inputs of regional groundwater, creating a mosaic of phosphorus (P) availability. Over the ensuing decades, these lowland tropical streams have been used as a natural laboratory to understand the role of P-availability on ecosystem processes. From 2005-2010, we found that the insect community in these high-P streams was enriched in body P-content, and that chironomid assemblages were physiologically adapted to high-P food resources. We also showed that, in low-P streams, excretion by fishes that feed on terrestrial insects provides an important source of P to the ecosystem. An experimental 8-year P addition to a low-solute headwater stream showed that sediment retention was a significant long-term sink for added P, dampening the biotic effects of P loading and altering the timing and quantity of P exported downstream. Fifteen years later, this work has provided important examples for the application of ecological stoichiometry theory to streams, and teaching resources developed from this research are now being used to train the next generation of stream ecologists.