Yoiks:  A southern Idaho reservoir is contaminated with mercury at levels up to 180 times higher than those found in lakes in the northeast US.  From the Idaho Statesman:

"Nobody’s ever seen a hot spot like this before," said Mike DuBois, an air quality analyst at the Idaho Department of Environmental Quality.

The likely culprit:  four gold mines across the border in northern Nevada, which emitted 15,000 pounds of mercury in 2002 alone.  Of course, the mines are patting themselves on the back for reducing their  mercury releases to just a couple of tons per year as of 2004.  But that’s still a huge amount of mercury for just a handful of mines.  The 1,000-odd coal-fired electricity industry generators in the US emit a total of 48 tons of mercury each year; so those few Nevada mines make up a disproportionately large share of the nation’s total mercury output.

And just in case you need a reason to care about this: mercury contamination early in life can knock a few points off a kid’s IQ, which in addition to being grossly unfair, costs nearly $9 billion a year in lost earnings.