Participatory modeling has grown in popularity in recent years with the acknowledgement that stakeholder knowledge is an essential component to informed environmental decision-making. Including stakeholders in model building and analysis allows decision-makers to understand important conceptual components in the environmental systems being managed, builds trust and common understanding between potentially diverse sets of competing groups, and reduces uncertainty by mining information that might not otherwise be a part of scientific assessment performed by experts alone. Software that facilitates the integration and analysis of stakeholder knowledge in modeling, however, is currently lacking. In this paper we report on the design and anticipated use of a participatory modeling tool based in fuzzy-logic cognitive mapping (FCM) called 'Mental Modeler' which makes the mental models of stakeholders explicit and provides an opportunity to incorporate different types of knowledge into environmental decision-making, define hypotheses to be tested, and run scenarios to determine perceived outcomes of proposed policies.