The St. Johns Bayou and New Madrid Floodway project was first proposed in 1954 as a means of protecting an area of rich Missouri agricultural land from frequent flooding. The price tag for the quarter-mile-long project now stands at $165 million.
Environmental groups have long opposed the project, saying it would threaten a wetland and habitat for fish and wildlife. Nearly 100 environmental groups sent a separate letter to Obama on Tuesday renewing that concern.
The Army Corps of Engineers says the levee would generate about twice the economic benefit of the construction cost.