The discharge of Fukushima contaminated water into the Pacific Ocean began in the summer of August 2023. This paper proposes the concept of “treated (but still contaminated) water” from the perspective of critical geopolitics to address the issue of Fukushima contaminated water discharge to the sea. First, it revisits the scientific debates surrounding contaminated water and the process of demarcating contaminated areas in Chernobyl (soil contamination) and Fukushima (marine discharge). Second, it analyzes the Japanese government’s public service announcements and the Ministry of Economy, Trade and Industry(METI)’s public opinion polls and promotion of agricultural and fishery products as a public ascription of biological citizenship. It also examines the conservatization of the media, even those critical of nuclear power, following China’s suspension of imports of Japanese seafood. Third, it analyzes Japanese Consumers’ Co-operative Union and public comment that raised issues of national, regional, community, and procedural democracy in decision-making. Finally, we analyzed the implications of the treated (contaminated) water lawsuit, which raised the issue of violations of the London Convention. Through these analyses, we examined the causes and development of the Fukushima contaminated water problem and the search for alternatives in the medium and long term.