Moments after opening the spillway, a wall of water three times the weight of Niagara Falls spewed into smaller waters and tributaries, changing the reality for residents in smaller towns farther south of the river.
Army Corps of Engineers New Orleans District Commander Colonel Ed Fleming told ABC News that it will still be weeks before engineers begin to assess the new landscape and declare emergency warnings.
"We want to make sure that folks have the understanding that water's coming their way and they need to evacuate," he said.
The powerful water could affect nearly 25,000 people and hundreds of thousands of acres of farmland before communities see the Mississippi start to crest. Engineers say nearly 4,000 residents have already been affected.
In St. Mary's Parish, moving vans crowded the streets. Resident Dr. Ronald Perry said he'd thought he would live out his retirement in his quiet town, but now his life has been turned upside down.
"It looks like a battlefield across the street, it's ... something we never would have expected," he said.
While most residents were moving to safety, some recreational fisherman are waiting to see which direction the floodgates push the water and critical species within it.
The opening of the spillways, fishermen told ABC News, could push salt waters closer to the shoreline, creating a bonanza of crawfish and trout within greater reach. However, they said, the rivers could divert in a new direction, pushing fish farther downstream and creating a huge deficit for the entire season.
The spillways have already closed oyster beds, which engineers say could threaten the oyster trade for this season, according to state officials.
The crest in these areas could last between seven to 10 days. Officials could decide to open more possible floodgates, placing surrounding towns in disarray.