<p>The tailings storage facility iterative simulation model (TSFISM) is a dynamic water-balance simulator that was developed in Microsoft Excel 365^®. The TSFISM workbook has a user-friendly interface that incorporates all natural and mine-related inflows and outflows to and from a tailings storage facility (TSF). TSFISM simulates TSF pool stages and free-water volumes by solving iteratively for changes in pool stage and volume at the end of each time step. TSFISM reliably accounts for the dynamic changes in TSF-pool geometry during operations by distributing tailings volumes proportionally by tailings-production mass. Free-water volumes are calculated from frequent bathymetric surveys and tailings production, which negates complexities associated with variably saturated flow, computation of water entrainment, and dry/wet beach evaporation. TSFISM predicts bathymetric surveys at user-specified time intervals for future scenarios. A regression between cumulative tailings production and measured pool-bottom elevations is used to estimate future bathymetries from projected tailings production. TSFISM also dynamically simulates TSF beach and catchment runoff, allowing the beach area, catchment area, and runoff coefficient to vary with time. TSFISM has robust capabilities to simulate a variety of site-specific TSF conditions and can run an unlimited number of water-management scenarios under climatic uncertainty.</p>