Since 2009, the Johor Straits, a channel between Singapore and Malaysia, has been experiencing episodic harmful algal blooms (HABs). Microscopic algal species are the base of marine food chains but, in high densities, they can poison or suffocate all other organisms within range. HABs have caused massive losses to aquaculture industries and the decimation of coastal and marine ecosystems, putting scientists under pressure to understand and predict their emergence. Scientists, however, are confounded by why it took so long for a bloom to happen in the highly anthropogenic Straits. Further complicating scientific inquiry are the political tensions between Singapore and Malaysia over pollution in the Straits. Meanwhile, residing in the Straits are communities of fish farmers, fishermen and indigenous Orang Seletar, whose livelihoods are closely tied to various environmental conditions, ecosystems, and organisms that have been associated with algal diversity, growth, and decline. The historical experiences and everyday activities of these communities may reveal clues for what caused or delayed HABs in the Straits. Working with coastal communities, marine scientists, and policymakers, this project will employ a range of ethnographic methods to understand the critical thresholds of human disturbance beyond which HABs became possible and the forms of social and environmental resilience that delayed them. In doing so, I seek to re-think how we study social dimensions of environmental degradation, by exploring the human and nonhuman interactions that mediate the increasingly thin line between chronic degradation and acute ecological crises.