(CNN) -- The U.S. Army Corps of Engineers began explosions Monday night at the Birds Point-New Madrid levee at the confluence of the Ohio and Mississippi rivers.
The explosions, near the southern border between Missouri and Illinois, marked the start of a three-stage process to intentionally breach the levee -- and, in the process, pave the way for tons of water to flood 130,000 acres of Missouri farmland -- to alleviate pressure caused by historically high water levels in the rivers.
At 5 p.m. Monday, the water level outside Cairo, Illinois, was 61.44 feet -- well above the flood stage of 40 feet -- according to the National Weather Service. Maj. Gen. Michael Walsh ordered the intentional breach.
"(The system) continues to be under enormous and unprecedented pressure," said Walsh, the president of the Mississippi River Commission. "Because of that ... I've ordered the district commander to operate the project."
Walsh said that historic and still-rising flood waters made it imperative to begin the explosive operation as soon as possible. The multistage process is expected to continue through Tuesday.
Missouri Attorney General Chris Koster's office tried to block the move, challenging the Corps' authority to breach the levee. But the U.S. Supreme Court, in a ruling from Justice Samuel Alito, denied Missouri's bid.
On Monday, Gov. Jay Nixon issued a statement saying he had talked with Walsh about the attempt "to relieve pressure on other parts of the levee system and save lives." He said Missouri authorities are ready for the blast and subsequent flood.
"I urge Missourians to continue to cooperate fully with state, county and local law enforcement, as they have at every stage of this process," Nixon said. "Together, we will ensure that Missouri families stay safe in the coming days. And together, we will recover and rebuild."
Without an intentional breach, authorities had warned of massive flooding that could wipe out Cairo. Already, Cairo's mayor ordered the city's 2,800 residents to evacuate.
Walsh acknowledged the human dimension of his plan, which has irked many in Missouri, where hundreds more have been evacuated. Nixon has estimated that it will take tens, if not hundreds of millions of dollars to recover property and rebuild lives as the water rushes through the floodway, including washing out farmland he described as "literally the most productive part of our continent."
"It's a heart-wrenching story," Walsh said. "It takes a long time to recover from something like this."
He said the fate of Cairo was just one of many factors in his decision, saying he hoped the move would alleviate issues throughout the Mississippi River system. Water levels and flooding have hit record highs in many spots, putting severe strains on systems meant to prevent uncontrolled floods and the resulting loss of life and property.
With rain continuing to fall and water levels continuing to rise, Walsh said the situation would only get worse without drastic action.
"Nobody has seen this type of water in the system," he said. "This is unprecedented."
And he did not rule out similar moves elsewhere, including possibly more purposeful explosions at other levees along the Mississippi and its tributaries.
The area, in Missouri's so-called "Bootheel," is one of four floodways along the system that could be opened up. Walsh said he expected the Birds Point-New Madrid levee breach will cause river crests to drop three to four feet "for a few days," even as he voiced concerns that water levels could very well rise again.
"This doesn't end this historic flood," said Walsh. "This is not going to be over when we operate this."