A different concern about water quality arose when mercury was discovered in fish during the 1980s. Because mercury is damaging to humans, warnings were posted for fishermen that cautioned against eating fish caught in South Florida, and scientists became alarmed when a Florida panther was found dead near Shark River Slough with mercury levels high enough to be fatal to humans.[36] When mercury is ingested it adversely affects the central nervous system, and can cause brain damage and birth defects.[37] Studies of mercury levels found that it is bioaccumulated through the food chain: animals that are lower on the chain have decreased amounts, but as larger animals eat them, the amount of mercury is multiplied. The dead panther's diet consisted of small animals, including raccoons and young alligators. The source of the mercury was found to be waste incinerators and fossil fuel power plants that expelled the element in the atmosphere, which precipitated with rain, or in the dry season, dust.[36] Naturally occurring bacteria in the Everglades that function to reduce sulfur also transform mercury deposits into methylmercury. This process was more dramatic in areas where flooding was not as prevalent. Because of requirements that reduced power plant and incinerator emissions, the levels of mercury found in larger animals decreased as well: approximately a 60% decrease in fish and a 70% decrease in birds, though some levels still remain a health concern for people.[36]