Nowhere are the environmental, social, and political effects of climate change more visible than in the world’s oceans. This dissertation demonstrates how changing sea environments reshape experiences of health, risk, and identity in the Caribbean, where longstanding communities of diver fishermen contend with shifting ecologies and depleted fish stocks, alongside regional conservation policies that further marginalize sea-dependent communities. Based in 24 months of ethnographic research with fishing communities on the northern coast of the Dominican Republic, I show how notions of human and environmental health are deeply entangled through longstanding ecological relations, national politics, and increasing instances of injury at sea. I conducted participant observation and semi-structured interviews with diver fishermen and conservation officials. By describing life in a rural fishing province, chronic instances of decompression sickness, and how policies of ocean conservation unfold in relationships between fishermen and state officials, I show how risk, injury, and political marginalization are the predominant conditions of daily life for those who depend on the sea. At its core, this dissertation seeks to explore the effects of changing environments on people, their perceptions (chapter 1), their bodies (chapter 2), their identities (chapter 3), their national contexts (chapter 4) and their broader legal status (chapter 5). This study shows how risk and political marginalization come to characterize human-environment relations through changing marine environments, the politics of ocean conservation, and longstanding structures of power that shape inequality in Caribbean communities.This dissertation links crucial scholarship in medical anthropology and environmental anthropology, showing how human and environmental health are entangled through embodied experiences in shifting ocean ecologies. My findings demonstrate that attempts to create policies conserving vulnerable marine environments and resources actually magnify the ways coastal communities experience changing climates, both in terms of their corporal health, economic security, and legal rights to newly protected areas.