This essay argues that society's understandings of environmental and public health threats are dangerously compromised by expert systems that create and legitimate those understandings. Principal among those expert systems, scientific disciplines and regulatory agencies reinforce expectations and practices for producing knowledge in ways that minimize the ecological and socio-historical contexts in which that knowledge is created. The result, in effect, is organized ignorance—a system of knowledge production that articulates risk in ways that leave much potential knowledge “undone.” We use the organization of environmental testing in Orleans Parish following Hurricane Katrina to illustrate these claims.