Two evolving dynamics are a feature of environmental decision making. First the movement to empower participants in developing and implementing solutions and second the use of models as tools to inform decisions within complex scenarios. The co-evolution of these dynamics aids stakeholders with different perspectives to understand the system in question. This study examined these movements focusing on the ways in which the decision to use computer models influenced the definition of the issue, the allocation of resources, the group structure and the decision process, by using qualitative methods (semi structured interviews) in two case studies from the Great Lakes system: Salmon Stocking in Lake Ontario (1992 – 1997) and Lake Ontario-Saint Lawrence River Study (2000 – 2007). This study found that the unilateral selection of a modeling framework constrains the decision process and an agreed definition of the issue sets for a smother process. The value of a model is not only reflected in its output but also in the process during its construction.