Mercury is a metal that has several forms. Most commonly, people recognize mercury as the shiny, silver-white fluid in thermometers. Methylmercury is the kind of mercury that gets into fish. In water, the inorganic form of mercury is converted to methylmercury by bacteria or chemical reactions.
Mercury contamination is a worldwide problem.
It can come from many sources. It occurs naturally in the environment in rocks, soils, water and air. It can come from industrial pollution, especially the burning of coal and other fossil fuels and from burning household or industrial wastes. Mercury compounds settle into sediments of lakes, rivers and oceans. Fish primarily absorb methylmercury from the prey they eat.