TO MISSOURI lawmakers, it’s a common-sense community development project. To what seems like almost everyone else, it’s a bizarre waste of taxpayer money and an ecological disaster that a few members of Congress refuse to drop.

The New Madrid Floodway is a strip of land along the Mississippi River in Missouri’s “bootheel.” The Army Corps of Engineers dumps water into it when the river threatens to flood the city of Cairo, Ill., as it did in 2011. People nevertheless farm the land in the floodway, and they want the Corps to help them do it. Backed by their representatives in Congress, they demand a $165 million project to, yes, prevent too much flooding in the floodway.

There is a 1,500-foot gap in the local levee at the bottom of the floodway. That gap allows water to exit when the Corps purposely inundates the area. But the gap also allows water into the floodway at other times, resulting in unintentional flooding. Residents want the Corps to close the gap and blow a hole at the bottom of the levee when it needs to use the floodway. In years in which the floodway isn’t needed — most, so far — that would increase agricultural yields and, no doubt, local land values. In other words, they want the federal government to spend taxpayer money encouraging economic activity in a zone it is obligated to flood during high-water events. It should be no surprise that the locals are putting up none of their own cash to pay for the project. Also unsurprising is the alarm of Cairo’s mayor, who worries that building up the floodway meant to protect his city would make it harder to strategically inundate that area and so spare his residents.

Taxpayer advocates and environmentalists are raising the alarm. The project would drain a whopping 41,000 acres of wetlands in one of the last places along the lower Mississippi that still has them. When the water flows through that gap in the levee, fish and waterfowl follow along, using the habitat to spawn and feed. The Corps has claimed that it can offset the damage, but environmentalists — and regulators at other government agencies — have strongly disagreed with its assessments.

The New Madrid Floodway project has been on the table since at least 1954, and it nearly got built decades later — until a federal judge tossed it in 2007. The corps is completing a new analysis — its seventh — claiming the plan would result in modest economic gains for those in the area, and Sen. Roy Blunt (R-Mo.) is threatening to hold up the confirmation of President Obama’s next Environmental Protection Agency chief if the administration doesn’t proceed quickly.

Instead, Mr. Obama should finally kill the ­project.