The federal agency, acting under the Clean Water Act, said it decided to prohibit construction because of the environmental impact of the project on tens of thousands of acres of wetlands and other water resources.

"Together with our state and federal partners we can improve flood protection and ensure environmental protection," said Benjamin Grumbles, the EPA's assistant administrator for water. "We're helping to identify a better project that reduces flooding, protects the environment and saves taxpayer dollars."

The Yazoo pumps project, authorized in 1941, was an effort to reduce flooding in Mississippi, between the Yazoo and Mississippi rivers.

The $220 million project would have had an annual operational cost of more than $2 million, with its primary component being a 14,000 cubic feet a second pumping station to move rainwater from the area during high water events on the Mississippi River.

The EPA said it will work with other federal and state agencies to identify an alternative project.