We investigated how phytoplankton, epiphyton, and epipelon respond to short-term nutrient enrichment and its interruption in a mesocosm experiment in a mesotrophic shallow lake. Enrichment increased phytoplankton biomass but reduced epiphyton and had little effect on epipelon. After stopping enrichment, phytoplankton declined while epipelon increased. Enrichment also altered community structure, favoring bloom-forming and shade-adapted species. The nutrient enrichment associated with phytoplankton blooms can compromise periphyton function by reducing biomass, diversity, and altering species composition in shallow lake ecosystems.