Mercury is an important environmental contaminant with a complex chemistry cycle. The SERAFM model (SERAFM) incorporates the chemical, physical, and biological processes governing mercury transport and fate in a surface water body including: atmospheric deposition; watershed mercury transport, transformations, and loadings; solid transport and cycling within the water body; and water body mercury fate and transport processes. SERAFM is comprised of a series of sub-modules that are linked together in series, so that each part is viewed as a building block within the general modeling framework. SERAFM estimates exposure mercury concentrations in the sediment, water column, and food web, and calculates hazard indices for exposed wildlife and humans. Because mercury risk assessments are complicated due to the different source types, that is, from historical loadings of mercury from current atmospheric deposition and watershed loadings, SERAFM simultaneously calculates exposure conditions for three different scenarios at any given site. These are: (1) the historical case of mercury-contaminated sediments; (2) suggested clean-up levels necessary to protect the most sensitive species, if possible; and (3) background conditions that would be present if there were no historical contamination. The sub-modules within SERAFM include: mercury loading (watershed and atmospheric deposition); abiotic and biotic solids balance (soil erosion, settling, burial, and resuspension); equilibrium partitioning; water body mercury transformation and transport processes; and wildlife risk calculations. The spreadsheet structure of SERAFM permits dismantling and reassembling of specific sub-modules to allow model flexibility and to maintain model transparency.