["Singapore Journal of Tropical Geography, EarlyView. ", "\nDespite lacking a permanent administrative structure, West Malaysia's Klang Valley constitutes the territorial and material basis upon which state spatial strategies have been constructed. However, the Valley's technocratic origins have often received insufficient attention in contemporary scholarship, thus obscuring its emergence as a regional development scheme, fundamentally shaped by Cold War‐era decolonization, anxieties over natural disasters, and postcolonial communal tensions. By viewing the Valley's production through the lens of hydro‐modernization, we apply a theoretical framework combining enclosure and racial governmentality to comparatively analyse two developmental studies: (1) the Klang Valley Plan; and (2) the Klang Valley Regional Planning and Development Study. Our analysis centres on how approaches to regional development were fundamentally transformed in the 1970s in response to Singapore's separation from Malaysia, top‐down imperatives to engineer national unity in the wake of the 1969 racial riots, and severe flooding that inundated Kuala Lumpur and other parts of West Malaysia. In response, ecological considerations were displaced in favour of conceptualizing the Valley as an abstract space, upon which the racialized ideological goals of the New Economic Policy could be spatially operationalized, while an emergent regime of environmental governance simplified the ecological complexity of the underlying Klang River basin in favour of hydrological engineering. We conclude by calling for greater sensitivity to how the Valley's development was rooted in racialized political considerations and changing conceptions of (post)colonial environments. In doing so, we offer a more critical interrogation of race, environment, and nationhood in the Malaysian Anthropocene.\n"]