CAIRO, Ill. — Local officials in this southern Illinois river town, along with environmentalists and conservationists from throughout the Midwest, have petitioned the U.S. EPA in their latest attempt to stop an expansion of the New Madrid Floodway levee system.

That system was prominent in spring 2011 when a swollen Mississippi River threatened to flood much of Cairo and other areas further north from where the Mississippi and Ohio rivers converge.

To alleviate the pressure on upriver towns, the U.S. Corps of Engineers blasted three holes in parts of the Birds Point levee, sending floodwaters rushing onto about 130,000 acres of prime Missouri farmland.

Growers, who opposed the blasting at the time and unsuccessfully sought an injunction from the U.S. Supreme Court to stop it, watched as a season’s worth of crops were washed away in a matter of hours. The floodway, maintained by the Corps since the early 1900s, only has been activated on two occasions to relieve flood pressure, in 1937 and 2011. The levee system protects what is largely considered some of the richest farmland in the United States.

The Corps has since rebuilt the Birds Point levee and adjacent ditches at a cost of about $50 million; the resulting crop losses were estimated at more than $50 million based on insurance payments dispensed to growers within the six counties within the floodway.

The entire floodway project, with additional levees yet to be completed, was first proposed in 1954 and has remained controversial since. The latest price estimate to complete it as originally planned is pegged at about $165 million.

Opponents to its completion now have filed letters with the EPA and the Obama administration asking the EPA veto the project based on an obscure provision of the 1972 Clean Water Act, which gives the agency veto authority if it determines that “unacceptable adverse affects” would result if the project were completed.

Given the widely accepted belief that Cairo would have sustained significant flood damage with the levee breach in 2011, city leaders argue expansion of the levee system is unnecessary and puts areas north of the river confluence at continued risk.

“Under any scenario, this project … should be vetoed,” said Melissa Samet, an attorney with the National Wildlife Federation. She also suggested a levee expansion would make it much more difficult to activate the floodway in future flooding events.

“If Cairo floods during a catastrophic Mississippi River flood, Cairo’s going to be gone,” she said.

But Danny Ward, the floodway project manager based at the Corps’ Memphis District, said Corps studies show an expansion won’t increase flood risk to upstream areas. “We definitely understand their concern,” he said. “However, the construction of this project is not going to hinder any future operation of the floodway.”

He noted one recent Corps study shows the project overall provides twice as much economic benefit to the region than without it, particularly because of the fertile soil. The EPA has until this summer to act on the groups’ request, and the Corps expects to conduct a final public hearing before finalizing any work, assuming Congress appropriates funds for the project, Ward said.