The causative agent is methylmercury. Methylmercury produced in the acetaldehyde acetic acid facility of Shin Nihon Chissos Minamata factory was discharged in factory wastewater... Minamata disease patients last appeared in 1960, and the outbreak has ended. This is presumed to be because consumption of fish and shellfish from Minamata Bay was banned in the fall of 1957, and the fact that the factory had waste-treatment facilities in place from January 1960. The conclusion contained many factual errors: eating fish and shellfish from other areas of the Shiranui Sea, not just Minamata Bay, could cause the disease; eating small amounts, as well as large amounts of contaminated fish over a long time also produced symptoms; the outbreak had not, in fact, ended in 1960 nor had mercury-removing wastewater facilities been installed in January 1960. Nevertheless, the government announcement brought a feeling of relief to a great many victims and their families. Many felt vindicated in their long struggle to force Chisso to accept responsibility for causing the disease and expressed thanks that their plight had been recognised by their social superiors. The struggle now focused on to what extent the victims should be compensated. Struggle for a new agreement
In light of the government announcement, the patients of the Mutual Aid Society decided to ask for a new compensation agreement with Chisso and submitted the demand on 6 October. Chisso replied that it was unable to judge what would be fair compensation and asked the Japanese government to set up a binding arbitration committee to decide.
Masazumi Harada has said that, "It may sound strange, but if this second Minamata disease had not broken out, the medical and social progress achieved by now in Kumamoto... would have been impossible. "Around this time, two other pollution-related diseases were also grabbing headlines in Japan. People with Yokkaichi asthma and itai-itai disease were forming citizens groups and filed lawsuits against the polluting companies in September 1967 and March 1968, respectively. As a group, these diseases came to be known as the four big pollution diseases of Japan.Slowly but surely, the mood in Minamata and Japan as a whole was shifting. Minamata patients found the public gradually becoming more receptive and sympathetic as the decade wore on. This culminated in 1968 with the establishment in Minamata of the Citizens Council for Minamata Disease Countermeasures, which was to become the chief citizens support group to the Minamata patients. A founding member of the citizens council was Michiko Ishimure, a local housewife and poet who later that year published Pure Land, Poisoned Sea: Our Minamata disease, a book of poetic essays that received national acclaim. 1969–1973
Official government recognition
Finally on 26 September 1968 – twelve years after the discovery of the disease (and four months after Chisso had stopped production of acetaldehyde using its mercury catalyst) – the Japanese government issued an official conclusion as to the cause of Minamata disease:

Minamata disease is a disease of the central nervous system, a poisoning caused by long-term consumption, in large amounts, of fish and shellfish from Minamata Bay.