The Watershed Management Optimization Support Tool (WMOST) is a decision support tool that facilitates integrated water management at the local or small watershed scale. WMOST models the environmental effects and costs of management decisions in a watershed context that is, accounting for the direct and indirect effects of decisions. The model considers water flows and water quality. It is spatially lumped with options for a daily or monthly modeling time step. The optimization of management options is solved using nonlinear programming. WMOST is intended to be a screening tool used as part of an integrated watershed management process such as that described in EPA’s watershed planning handbook (EPA 2008). WMOST serves as a public-domain, efficient, and user-friendly tool for local water resources managers and planners to screen a wide range of potential water resources management options across their jurisdiction for cost-effectiveness and environmental and economic sustainability (Zoltay et al., 2010). Practices that can be evaluated include projects related to stormwater (including green infrastructure [GI] and combined sewer overflow (CSO) systems), stream restoration, water supply, wastewater and land resources such as low-impact development (LID) and land conservation. WMOST can aid in evaluating LID and green infrastructure as alternative or complementary management options in projects proposed for State Revolving Funds (SRF). In addition, the tool can enable assessing the trade-offs and co-benefits of various practices. In WMOST v3, the Baseline Hydrology and Loadings and Stormwater Hydrology and Loadings Modules assist users with input data acquisition and pre-processing. The Combined Sewer Overflow (CSO) Module allows for the evaluation of management options to minimize the number of CSO events. The Flood Module allows the consideration of flood damages and their reduction in assessing the cost-effectiveness of management practices. The target user group for WMOST consists of local water resources managers, including municipal water works superintendents and their consultants.