Radioactive water from the Fukushima Daiichi Nuclear Power Plant in Japan began being discharged into the Pacific Ocean on 11 March 2011, following the Fukushima Daiichi nuclear disaster triggered by the Tōhoku earthquake and tsunami. Three of the plant's reactors experienced meltdowns, leaving behind melted fuel debris. Water was introduced to prevent the meltdowns from progressing further. When cooling water, groundwater, and rain came into contact with the melted fuel debris, they became contaminated with radioactive nuclides, such as iodine-131, caesium-134, caesium-137, and strontium-90.