Responding to concerns that industrial emissions from the United States were causing highly acidic precipitation that would damage forests and ruin fisheries, particularly in the northeast United States and Canada, the Environmental Protection Agency administered the National Acid Precipitation Assessment Project (NAPAP), a ten-year scientific inquiry of unprecedented scale that cost $540 million and concluded in 1990.

But NAPAP found that over half of the dead, acidic lakes were not located in the northeast at all but in Florida, which does not receive high rates of acid rain. Despite dire assertions about the state of northeastern lakes, it turned out that only about one-fiftieth of one percent of the fresh water in the eastern United States was "acid-dead," with a pH of 5.0 or lower. NAPAP concluded that acid rain may have caused marginal environmental problems such as stress to certain high-altitude tree stands, which itself could also be explained by the presence of disease or parasites. NAPAP also noted huge variations in acid precipitation around the world, with some Pacific islands receiving naturally high levels of acid rain due to the presence of carbonic acid derived from carbon dioxide. Of the acids derived from industrial emissions, NAPAP was mostly concerned about sulfuric acid, since nitric acid is readily absorbed by trees as a nutrient.

Soil scientist and NAPAP participant Edward Krug concludes that the major factor causing certain lakes to become acidic is not acid precipitation but the alkalinity of the surrounding soil. Krug notes that normal rainfall has a pH of 5.0, which most species of fish cannot survive in, but most watersheds are buffered by lime-like alkaline substances that underly rivers and lakes. The high acidity of lakes in the Adirondacks and Nova Scotia results from a lack of this natural buffering. A multimillion-dollar survey also found that biological factors, such as the presence of acid-producing sphagnum mosses, also contributed to the dearth of alkalinity in the Adirondack watershed.

Then why was there such good fishing in the Adirondacks as recently as 100 years ago? Even President Theodore Roosevelt prized the region as a vacation site because the fish were so plentiful. Krug concludes that this represents a recent anomaly and that originally the lakes were acid-dead. The Iroquois word "Adirondack" literally means "bark-eater," which suggests poor fishing, and initial European settlers also found it very difficult to stock local lakes with fish. Core samples from lake bottoms also revealed the lakes to be historically acidic.

However, during the latter half of the 19th century the Adirondack area became a major center for the wood industry, which at the time entailed devastating clear-cutting that was accompanied by massive forest fires. Much of the naturally acid-producing plant life was eroded away and replaced by alkaline ash from the forest fires, runoff from which caused the local watershed to become inhabitable for sport fish for a time. But this severe environmental disturbance in turn led to local conservation measures when the government bought the damaged land from the lumber companies and made it into a park, a measure that after a time caused the watershed to return to its natural acidic state. Krug found the same scenario of low-alkalinity soil, and the same history of logging followed by conservation, also applied to Nova Scotia as well as Scandinavia, where the recent acid-lake problem had been blamed on industrial emissions from Great Britain and central Europe.

Krug also concluded that if people wanted those lakes that were acidic to support wildlife, the best way to do so would be to seed targeted watersheds with lime. Krug determined that all acidic lakes in New York and New England could successfully be limed for under $500,000 a year, compared to the billions of dollars it would cost to reduce acid rain emissions, which evidence showed would not work anyway. And already on Cape Cod, the National Park Service has resisted pressure to "improve" acid lakes for fishermen, in favor of its environmental mandate to preserve the natural ecosystem of its parks.

[Ed.: Acidity and alkalinity are measured on the logarithmic pH scale in units from 0 to 14, with 0 representing extreme acidity, 14 as extreme alkalinity, and 7 as neutral. Each pH unit represents a ten-fold increase in concentration, so a pH of 4.0 (as in a pear) is ten times more acidic than pH 5.0 (as in tea).

Ironically, regional acid precipitation intensified following local environmental efforts in cities like Pittsburgh and Cleveland to spread out pollution more widely with tall smokestacks and also to reduce soot emissions, which are alkaline and effectively neutralize the acids formed by burning fossil fuels.]

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