["The Geographical Journal, Volume 192, Issue 2, June 2026. ", "\nShort Abstract\nThis article examines the livelihood transformations and governance challenges faced by small‐scale fishers in Vietnam's Tam Giang–Cau Hai lagoon. Based on interviews and ethnographic fieldwork, it shows how fishers navigate declining resources, spatial competition and fragmented governance, while adaptation strategies often reproduce social inequalities. The study highlights sustainability transitions in coastal fisheries as contested political processes shaped by institutional complexity and spatial injustice.\n\nABSTRACT\nThis article examines the livelihood transformations and governance challenges of small‐scale fishers (SSF) in Vietnam's Tam Giang‐Cau Hai (TGCH) lagoon. Drawing on 47 semi‐structured interviews and extensive ethnographic fieldwork conducted in 2022, it reveals how fishers navigate overlapping pressures: declining stocks, pollution, spatial competition and fragmented institutional reforms. Although adaptation strategies like livelihood diversification and outmigration are common, they frequently exacerbate structural inequalities related to age, gender and socio‐economic status. We argue that state‐promoted alternatives, such as aquaculture and ecotourism, show limited success and often risk ‘pseudo‐diversification’ due to weak governance, uneven enforcement and spatial exclusion. Conceptually, this study advances an integrated framework combining wicked problems, livelihood adaptation, and spatial justice. It demonstrates that sustainability transitions in coastal fisheries are not merely technical challenges but contested political processes. By highlighting how institutional complexity and power asymmetries reproduce marginalisation, the study contributes to more grounded, justice‐oriented approaches to coastal governance in Southeast Asia.\n"]