In 2019, interdisciplinary teams of anthropology and environmental engineering PhD students went to Placencia Village, Belize to study stakeholder-driven issues related to coastal resilience. Our team explored wastewater management on a few of the more than 400 small cayes peppering the Belize Barrier Reef. These islands have transitioned from temporary sites for overnight fishers to crowded tourism destinations. Wastewater management has struggled to keep pace with these changes, spurring concerns about the health of the reef. Our task was to construct contextualized system dynamic models which would be useful to those concerned. Along the way however, we ran into tensions related to the underlying logic, and representations of people, in mathematical descriptions of social and technical configurations. This article lays out the context and lessons learned from our encounter with interdisciplinary systems modeling.