The , which is also called the , is a shallow semi-enclosed inland sea separating the island of Kyūshū

Kyushu

is the third largest island of Japan and most southwesterly of its four main islands. Its alternate ancient names include , , and . The historical regional name is referred to Kyushu and its surrounding islands....

 from the Amakusa Islands

Amakusa

Amakusa is a series of islands belonging to Japan, off the west coast of Kyushu . The biggest of the Amakusa islands is Shimoshima Island, 26.5 miles long and 13.5 miles in extreme width...

. It lies mostly within Kumamoto Prefecture

Kumamoto Prefecture

is a prefecture of Japan located on Kyushu Island. The capital is the city of Kumamoto.- History :Historically the area was called Higo Province; and the province was renamed Kumamoto during the Meiji Restoration. The creation of prefectures was part of the abolition of the feudal system...

 and at the southern end of the sea it also borders Kagoshima Prefecture

Kagoshima Prefecture

is a prefecture of Japan located on the island of Kyushu. The capital is the city of Kagoshima.- Geography :Kagoshima Prefecture is located at the southwest tip of Kyushu and includes a chain of islands stretching further to the southwest for a few hundred kilometers...

. To the north is the Ariake Sea

Ariake Sea

The is a body of salt water surrounded by Fukuoka, Saga, Nagasaki, and Kumamoto Prefectures, all of which lie on the island of Kyūshū in Japan. It is the largest bay in Kyūshū. Its deepest point is only about 50 m deep, and extreme tides exceed 4 m. It is used for aquaculture, with nori...

; to the south, the East China Sea

East China Sea

The East China Sea is a marginal sea east of China. It is a part of the Pacific Ocean and covers an area of 1,249,000 km² or 750,000 square miles.-Geography:...

. Cities of note that lie on the Yatsushiro Sea include Yatsushiro

Yatsushiro, Kumamoto

is a city located in Kumamoto, Japan.On August 1, 2005, the city merged with the municipalities of Izumi, Kagami, Sakamoto, Senchō and Tōyō to form the new expanded city of Yashushiro....

 itself and Minamata

Minamata, Kumamoto

is a city located in Kumamoto prefecture, Japan. It is on the west coast of Kyūshū. The city was founded on April 1, 1949.As of 2008, the city has an estimated population of 27,856 and the density of 171 persons per km²...

.

Mercury Pollution

The sea was heavily polluted

Pollution

Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...

 with mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 during the 1950s and 1960s from the Chisso Corporation's chemical factory in Minamata. This highly toxic

Toxicity

Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...

 chemical bioaccumulated

Bioaccumulation

Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...

 in shellfish and fish in the Yatsushiro Sea which, when eaten by the local populace, gave rise to Minamata disease

Minamata disease

', sometimes referred to as , is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death...

. The pollution disease was responsible for the deaths and disabling of thousands of residents, all around the Yatsushiro Sea. The marine ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

was also extensively damaged.