Tracking America's attitudes on eight environmental issues, Gallup's annual survey found a marked drop in the percentage of adults who said they worry "a great deal" about each particular topic.

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An annual Gallup survey finds Americans are less worried about environmental issues than they have been for the past two decades. Of the adults surveyed, 50 percent said they were very worried about the pollution of drinking water, a nine percent drop from last year.

For example, just 33 percent of those surveyed said they worry a great deal about the loss of tropical rain forests, compared with 42 percent who said they were in 2009.

Fifty percent of the adults surveyed this year said they are very worried about the pollution of drinking water, nine percentage points lower than in 2009's poll.

Similar trends held true for questions on the pollution of natural waterways, the contamination of soil and water by toxic waste, air pollution, the extinction of plant and animal species, the maintenance of the nation's supply of fresh water and the existence of global warming.

Gallup has conducted its survey since 1998. In this year's survey of 1,014 Americans, the polling organization said it saw record-low levels of concern in all but two of its categories -- global warming and maintenance of the fresh water supply.

The reasons for the decline in the percentages of Americans who expressed significant worry over the environment could be "due in part to Americans' belief that environmental conditions in the U.S. are improving," Gallup said on its Web site. "It also may reflect greater public concern about economic issues, which is usually associated with a drop in environmental concern."

Since the 1960s, the United States has passed significant environmental legislation. According to a study undertaken by the Environmental Protection Agency, the Clean Air acts of 1970 and 1977 dramatically improved air quality in the United States, saving hundreds of thousands of lives and improving overall health in the process. Likewise, the Clean Water Act of 1972 is credited with saving countless rivers and lakes from unregulated pollution.

But environmental groups say the Gallup poll's new numbers show an alarming disconnect from the problems that still face the planet.

"Tropical rain forests are still disappearing at a rate of 100,000 acres per day," Brianna Cayo Cotter, communications manager at the Rainforest Action Network, told AOL News. "Destroying the last great rain forests will likely result in worldwide drought that will have devastating economic and social ramifications."

Bob Deans, the federal communications director for the National Resources Defense Council, agrees with Gallup's conclusion that economic worries may be trumping environmental ones.

"The takeaway for me is that when people are struggling to feed their families, and are losing their homes, we'd expect to find people focused on those kinds of issues," Deans said. "At the same time, one-third of the Arctic sea ice is now gone, and, in part because of climate change, 8 million acres per year in the U.S. are now lost to wildfires, double the amount of a decade ago."

While Deans says he doesn't expect Gallup's findings to change much until the economy rebounds, he remains hopeful that an environmental agenda won't get lost in the shuffle in Washington.

"We could spend days talking about the list of things that are right now threatening the planet," Deans said