Threats to reefs from sedimentation and pollution from inland sources were modeled for over 3,000 watersheds discharging into the Caribbean. The model incorporates estimates of relative erosion rates across the landscape (based on slope, land cover type, precipitation during the month of maximum rainfall, and soil type) summarized by watershed to estimate resulting sediment delivery at river mouths. Sediment plume dispersion was estimated as a function of distance from the river mouth and calibrated against observed impacts of sediment on coral reefs.