This article charts the role damming practices play in rescaling the geopolitical interests of engineers in Guyana. It focuses on engineers’ responses to a disastrous flood in 1934, the first flood in their recorded history to compromise the East Demerara Water Conservancy. I argue that their responses rested on ideas about regionalism. By damming for local flood hazards, they recognized their failure to mobilize plantation agriculture which had provided an economic base for the rest of the (British) Caribbean. At the same time, their ideas about the formation of a regional political economy were subject to variation over time because of these flood hazards. Engineers, in other words, are political actors because they produce geographic frameworks for relating development to a changing climate. By tracing the work of engineers, this article is a modest attempt to understand what climate change can tell us about the pasts and futures of regional identity in the Global South.