Groundwater has long been ranked as a high priority research area by small island nations in the Pacific. It is the major source of freshwater on the atoll of Tarawa (Rep.of Kiribati) and its availability, quality, management and allocation are central to the atoll¿s sustainable development and poverty alleviation. From a modeling perspective, simulating freshwater lens behavior represents a challenge, as it requires sophisticated numerical models. Such models can hardly fit within an integrated management framework taking into account spatially distributed water use (e.g. wells, trees) and social interactions. Simple analytical solutions exist but they apply for steady-state conditions, verified only on an annual basis. Recent advances in the field of Distributed Artificial Intelligence have permitted the development of a Multi Agent System (MAS) approach, closely related to the problem of complexity. AtollScape uses MAS techniques to simulate water management and freshwater lens behavior on the Tarawa atoll. A distributed and nested structure is used to represent local inputs and uptakes, along with freshwater lens adjustments on a 10 day time steps.