Pharmaceuticals are important contaminants of concern in aquatic environments. One class of anti-depressant drugs, SSRIs are now detected in surface waters worldwide; however, the ecological impacts of SSRIs are not well understood. Using a laboratory and field based approach we were able to test the impact of SSRIs on ecosystem processes in artificial streams and detect and quantify pharmaceutical concentrations within stream insects in an urban creek influenced by waste water. Leaf packs and uncolonized rocks were added to artificial streams amended with environmentally realistic concentrations of SSRIs (20ng/L - 20ug/L). Biofilm colonization on rocks was affected by SSRIs; GPP was 60% lower on rocks in SSRI streams compared to controls. The low concentration of SSRI (20ng/L of fluoxetine) led to earlier dipteran emergence compared to the control and 20ug/L treatments. To further our understanding we detected and quantified amounts of pharmaceuticals within aquatic insects found downstream of a waste water treatment plant. These findings suggest that exposure to low concentrations of fluoxetine appears to affect aquatic biota and accumulation of pharmaceuticals in invertebrates has implications for higher trophic consumers. Indicating that these compounds are not necessarily toxic, but may have the capacity to alter ecosystem processes.