It’s not supposed to be like this. Though advisories about toxic mercury in fish have continued in Michigan and the surrounding Great Lakes, with recommendations to limit consumption of certain species to a few times per month, the amount of mercury found in fish tissues has dropped steadily over decades since the 1970s. That corresponded with the reduction of pollution coming from Midwestern smokestacks as regulations tightened, pollution prevention technology improved, and coal-fired factories and power plants went offline.