(CNN) -- A U.S. conservation group released a list Wednesday of what it says are America's 10 most endangered rivers, which face man-made threats from gas drilling and new dams to outdated flood management.
The list and accompanying report from American Rivers highlights the threats facing each waterway and urges the public to act to protect them.
Topping the list is the Upper Delaware River, which divides northeast Pennsylvania from southeast New York state and provides drinking water for 17 million people across both states. Natural gas drilling in the area threatens the river as a clean water source, the group said.
Gas drilling is also threatening the Monongahela River in southwestern Pennsylvania and northern West Virginia, the group said. The river, which is ninth on the list, provides drinking water for hundreds of thousands of people and is home to some of the East Coast's best fishing, whitewater boating, and wildlife, the group said.
Both the Upper Delaware and the Monongahela sit on an area called the Marcellus Shale, which lies beneath large parts of Pennsylvania, New York, and West Virginia at a depth of 5-8,000 feet, according to the Pennsylvania Department of Environmental Protection.
The shale is believed to hold trillions of cubic feet of natural gas. It has long been considered too expensive to access, according to the department, but recent technological advances and rising natural gas prices have rekindled an interest in drilling beneath the Marcellus Shale.
American Rivers says the natural gas extraction involves injecting chemicals into the ground, creating untreatable toxic wastewater. It urged the Delaware River Basin Commission not to issue new permits for gas drilling in the area until there can be a thorough study of its impacts, and it urged Congress to pass the Fracturing Responsibility and Awareness of Chemicals Act of 2009.
Along the Monongahela, American Rivers urged the Ohio River Valley Water Sanitation Commission and state authorities to prohibit pollution associated with the drilling.
The Pennsylvania Department of Environmental Protection says the wastewater from the drilling is treatable, and that disruption of water quality is "often rare and generally temporary."
Except when it's not... -Splashdown!
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