<p>The pit lake iterative simulation model (PLISM) is an iterative water-balance simulator that was developed in Microsoft Excel®. The PLISM workbook has a user-friendly interface that incorporates all natural and mine-related inflows and outflows to and from a pit lake. PLISM differs from previous water-balance approaches in data tabulation, pit-lake representation, and the solution method. User-defined data inputs can differ in time from PLISM time steps of lake stage and volumes. Unlike traditional pit-lake water balance models, PLISM is a transient model that simulates pit-lake stages and volumes by solving iteratively for changes in stage and volume at the end of each user-defined time step, rather than solving with forward differences. Stages and volumes are interpreted as a continuous function from the pit-shell geometry (i.e. stage-area-volume relation). PLISM also simulates highwall runoff as a function of pit-lake stage, where potential runoff from the catchment outside of the lake surface decreases as the lake stage increases. Highwall runoff is estimated with the curve number approach, which provides a physically defensible and climate-responsive framework for highwall runoff, greatly reducing uncertainty in this user-defined parameter. A simplified form of the Jacob and Lohman (1952) equation simulates groundwater exchange. PLISM was validated with the development of pit-lake models in semi-arid (Lone Tree Mine, Nevada, USA) and humid (Buzwagi Mine, Tanzania) climates, as examples. PLISM robustly simulates any site-specific pit-lake condition and an unlimited number of water-management scenarios that account for future climatic uncertainty.</p>