Environmental planning and decision-making processes are difficult, because they involve the evaluation of several alternatives in terms of multiple non-commensurate criteria, and a choice must be made considering the points of view of many different stakeholders with conflicting preferences. Much of the associated information can be highly imprecise or uncertain. Successful multicriteria decision aid (MCDA) methods for such problems should be able to represent explicitly not only the criteria and preference information, but also the associated uncertainty. We describe how to represent imprecise and/or uncertain criteria measurements and stakeholder preferences through probability distributions, and how to efficiently aggregate this information using stochastic simulation. As an example, we reanalyze the problem of choosing among different options for developing the Helsinki general cargo harbor. We perform the analysis by using the Stochastic Multicriteria Acceptability Analysis (SMAA-2) method with multivariate Gaussian distributions.