This paper evaluated user interaction with the graphical user interface of WRESTORE, an environmental decision support system (EDSS) for watershed planning that utilizes user ratings of design alternatives to guide optimization. The following usability metrics were collected for stakeholders as well as surrogates (who are often used for DSS development due to time or cost constraints): task times across sequential sessions, percentage of time spent and of mouse clicking in different areas of interest, and trends in self-reported user confidence levels. Task times conformed to theoretical models of learning curves. Stakeholders, however, spent 15% more time and made 14% more mouse clicks in information gathering areas than surrogates. Confidence levels increased over time in 67% of stakeholders, but only in 29% of surrogates. Relationships between time spent or mouse clicking events and confidence level trends indicated that confidence ratings increased over time for users who conducted more information gathering. This study highlights the importance of increasing user interactions within information gathering areas of an interface to improve user-guided search, and suggests that developers should exercise caution when using surrogates as proxies for stakeholders. It also demonstrates a quantitative way to evaluate EDSS that could assist others developing similar tools.