Methylmercury is a toxic compound formed when mercury, a heavy metal found in the environment, is converted by bacteria. This substance can accumulate in fish and other aquatic animals, making it a significant concern for those who consume seafood. When humans eat contaminated fish, methylmercury can enter the body and cause serious health issues, particularly affecting the nervous system. Due to its harmful effects, organizations like the Environmental Protection Agency (EPA) monitor methylmercury levels in water bodies. Pregnant women and young children are especially advised to limit their intake of certain fish to reduce exposure to this dangerous toxin.