It falls down directly onto waterways or is deposited on land where it can be washed into the water. Bacteria in the water cause chemical changes that transform mercury into a highly toxic form - methylmercury. Methylmercury accumulates in fish, with larger fish generally accumulating higher levels of methylmercury. The Environmental Protection Agency and States are working to reduce mercury pollution in the environment but because methylmercury is very persistent, it will be many years before methylmercury levels in fish are reduced. If you are pregnant or could become pregnant, are nursing a baby, or if you are feeding a young child, limit consumption of freshwater fish caught by family and friends to one meal per week.
Many states collect data on mercury levels in fish from local waters.
Check with your state or local health department for specific advice on waters where your family and friends are fishing. FDA advises that women who are pregnant or could become pregnant, nursing mothers and young children not eat shark, swordfish, king mackerel, or tilefish. FDA also advises that women of childbearing age and pregnant women may eat an average of 12 ounces of fish purchased in stores and restaurants each week. Therefore, if in a given week you eat 12 ounces of cooked fish from a store or restaurant, then do not eat fish caught by your family or friends that week. This is important to keep the total level of methylmercury contributed by all fish at a low level in your body.