Federal scientists studied mercury contamination in 21 Western national parks for years and last week announced bad news for Yosemite National Park -- the worst-tainted fish in the entire study was in a lake not far from Tioga Road.
One brook trout in Mildred Lake at 9,600 feet, southeast of picturesque Tenaya Lake, was actually unfit for human consumption -- the only fish in the study exceeding that danger level.
Overall, the U.S. Geological Survey study found 5 percent of the freshwater fish sampled in the 21 parks had levels of mercury that were high enough to endanger the lives of fish. It showed that even isolated, backcountry lakes in places such as Alaska have potential mercury problems.
For people, the toxic effects of mercury contamination are ghastly -- damage to the brain, kidney, and lungs. And the biggest source of the contamination for people and animals is consumption of fish.
So what is mercury doing in a pristine setting such as Yosemite?
Scientists don't know, but they also tested another high-country lake -- Spillway Lake, south of Mildred Lake -- and found very little mercury in the fish.
There are literally thousands of lakes and ponds in Yosemite, so it is hard to draw conclusions from one contaminated lake.
Where is the mercury coming from?
Mercury is a heavy metal that is increasing in the atmosphere. The sources are half natural -- volcanoes, for instance -- and human-generated from coal factories, cement plants and gold mining.
I do not know of past gold mining in the Yosemite high country.
About 100 miles south in Sequoia and Kings Canyon National Parks, scientists sampled four lakes where fish contained mercury levels below the average levels throughout the study.