This chapter examines the No Alto Maipo movement, a prominent case of socio-legal resistance against the construction of a hydroelectric project in central Chile. Situated in the Andean foothills near Santiago, the conflict mobilised a diverse coalition of actors concerned with environmental degradation, water scarcity, and the defence of ecotourism and local livelihoods. Unlike more remote socio-environmental struggles, Alto Maipo’s proximity to the capital and its ability to draw support from urban elites and environmental experts positioned it strategically within Chile’s legal and political opportunity structures. The chapter analyses how the movement framed its opposition through discourses of environmental justice and water rights, strategically combining legal action, public advocacy, and transnational networks. It assesses the use of litigation, expert testimony, and institutional engagement to delay and contest the project, while also interrogating the limitations of law as a tool for structural change. Ultimately, the chapter argues that the Alto Maipo case reveals both the strengths and constraints of legal mobilisation in contexts where corporate, financial, and political interests converge around environmentally harmful infrastructure.