Mercury pollution comes from coal power plants. Power plants are allowed, to some extent, to dump mercury and other pollutants into rivers, streams, and oceans. Most plants, you’ll notice, are located next to a river or a lake. Mercury is a toxic poison and can kill. It gets into our food supply, and is especially concentrated in fish. On December 16th, the EPA is expected to issue a ruling to lower the amount of pollution coal plants can dump into the environment.
Source: Sierra Club Mercury Awareness