Everybody knows national parks are going downhill. In fact, according to the gun lobby, people need a weapon handy in the parks to protect themselves, apparently from retired people and children tagging after their parents.

But who knew that some of the country’s highest and most isolated, pristine parks, including Glacier National Park in Montana, also have dangerous levels of pollutants in their lakes, plants and fish?

A six-year federal study of 20 parks stretching from Denali in Alaska to Big Bend in Texas found industrial contaminants galore, with eight of the parks (Including Glacier) having pollution in fish exceeding human consumption thresholds. The substances — 70 in all — include mercury produced by power plants, industrial chemicals such as PCBs, and pesticides.

Perhaps most galling, many of the pollutants don’t even come from nearby, but blow in from overseas. For instance, mercury from China is carried over the Pacific in clouds that rise when they reach western mountains, dropping their load. However, researchers also found substantial pollution from legal pesticides used near the parks, once again including Glacier.

The National Parks Conservation Association, a group that recently has led the protest against possible pollution of Glacier by mining activities in nearby British Columbia, called the report a wake-up call that should mobilize Congress to get tougher on air pollution.

We’ll see. But in the meantime, enjoy your happy, care-free vacation in our national parks.