This dissertation presents an in-depth study of one of the most controversial endangered species in United States history, and advances a theoretical framework for understanding the emergence of environmental problems in contemporary society. The delta smelt is a tiny fish found only in the Sacramento-San Joaquin Delta, the lynchpin of California’s water system. Legal protections of this once obscure species have made it a central player in California’s “water wars,” mobilizing political actors from the local level to the presidency. Drawing on archival sources, field observations, interviews, thousands of news articles, and social media data, I argue that far from being a mere conflict between interested actors, the contemporary controversy over the delta smelt emerged via sequential clashes among social domains which share jurisdiction over the nonhuman environment yet see “nature” in different ways. I call this process the “intervention cascade.” In the first chapter, “Becoming Endangered,” I show that it was only through the process of reengineering California’s river systems that the delta smelt came to be understood as a unique species, and one in danger of becoming extinct. Beyond simply being driven to near-extinction by California’s water infrastructure, the delta smelt was produced as an object of knowledge by that very infrastructural intervention in the first place. In the second chapter, “Constructing Environmental Compliance,” I theorize scientists as compliance professionals in relation to environmental law, tracing the changing relationship between science and law as the delta smelt’s population has declined. I explain why three distinct “compliance relations” became dominant at different junctures in the course of three decades’ worth of attempts to reconcile the delta smelt’s continued existence with the operation of California’s water infrastructure. In chapter three, “From the Water Wars to the Culture Wars,” I show how attempts to protect the species pursuant to the Endangered Species Act overflowed into a polarized public sphere. The controversy took on a life of its own, disconnected from and disproportionate to the delta smelt’s modest impact on water policy. Rather than the controversy being the straightforward result of constituencies pursuing their interests, the delta smelt’s status as a political symbol has been an important cause of the very constituencies that claim to have an interest in California water politics at all. Broadly, this research motivates a framework for understanding how the nonhuman environment mediates social conflicts, accounting for the dual realities of rapid environmental decline and intense disagreement over the meaning of nature.