America's grandest river is now one of the country's most endangered rivers, according to an annual report of the nation's waterways.

The health of the Mississippi River along its midsection, in an area known as the New Madrid Floodway, is being threatened by a new levee that poses a risk to wildlife habitats and overall safety downstream of the project, asserts the national environmental advocacy group American Rivers.

The Middle Mississippi, explains the group, is jeopardized by a proposed U.S. Army Corps of Engineers project that would cut off the last connection between the Mississippi River and its natural backwater habitat in the state of Missouri. The Corps proposes constructing a new 1,500 foot levee across the gap at the bottom of the New Madrid Floodway.

"Cutting off the Mississippi River's connection with its floodplain would destroy critical fish and wildlife habitat and put communities at greater risk of flooding," Eileen Fretz Shader, director of floodplain management for the organization, said in a news release. "The New Madrid Floodway project is completely at odds with modern floodplain management ... the 'America's Most Endangered Rivers' report is a call to action to save rivers that are at a critical tipping point."

The Mississippi River, said the American Rivers release, "once experienced seasonal floods that spread out over its floodplain, creating a mosaic of backwaters, wetlands, and sloughs. These periodic floods were the driving force behind robust and diverse ecosystems that were home to an amazing array of fish, birds, and wildlife."

Aside allowing the river to sustain vital environmental resources, the floodway also serves as a "relief valve" during large floods to permit water from the river to spread out instead of threatening upstream communities like Cairo, Ill., the release said.

Shader said American Rivers and its partners are calling the Corps to abandon the levee project, and urging the United States Environmental Protection Agency to veto the planned development if the Corps continues to move forward on it.

But, according to a story in the St. Louis Post-Dispatch, the floodway is prime farmland and landowners as well as community leaders have sought greater protection for the region's crops from flooding.

The Corps, which is reportedly finalizing an environmental impact study for the levee building project, estimates the project will supplement the region's economy with $15.5 million annually, as opposed to the $7.2 million in annual costs for the project.