(CNN) -- As the Mississippi River gushes downstream with no clear boundaries, flooding continues to deluge parts of Tennessee as residents farther south brace for what will come.
"When you see the Mississippi River and it's about two miles wide because it's lost its borders, it's sobering," said Tennessee Gov. Bill Haslam.
In some areas, murky brown water inundated entire neighborhoods, with only the roofs of buildings and treetops visible from the sky.
The Mississippi River is expected to crest about 14 feet above flood stage at Memphis as early as late Tuesday.
Shelby County Mayor Mark Luttrell urged residents to be calm and helpful during the crisis. Memphis is a city within the county.
"Our community is facing what could be a large-scale disaster," he said. "All of the mayors in the towns and cities throughout our county are staying in close contact with each other."
Residents of a trailer park were evacuated Saturday because of high waters, said Heather Reynolds, spokeswoman for the Memphis/Shelby County Emergency Management Agency.
Amid the calamity, some positive news surfaced.
The U.S. Coast Guard reopened a portion of the river near Caruthersville, Missouri, to limited commercial traffic late Friday.
"The Coast Guard will continue to work with the Army Corps of Engineers, waterway users and local communities to monitor river levels and restrict river traffic when necessary to protect the public," said Coast Guard Capt. Michael Gardiner.
This limited reopening was allowed for by a projected drop in the river crest from 49.5 feet to 48.1 feet, he said. The drop means one vessel can pass through the security zone at a time, Gardiner added.
Earlier in the day, the Coast Guard closed the stretch because of the possibility of vessel wakes topping the city's front flood wall, Chief Petty Officer John Edwards said.
Authorities in the Memphis area Friday warned residents of 1,089 homes that they were at risk from the coming floodwaters and urged them to leave.
Reynolds said about 350 people currently are in flood shelters, but the number will likely grow. Many residents may have moved in with families.
"We're hoping people will self-evacuate" in affected zip codes, she told CNN Saturday evening.
The flooding in the Mississippi and Ohio river valleys has forced people from their homes in Missouri, Illinois, Indiana, Tennessee, Kentucky and Arkansas. Now it has Mississippi and Louisiana under the gun.
The Army Corps of Engineers said that it would open a spillway 28 miles upstream from New Orleans to reduce the volume and velocity of the Mississippi River as the record level of water races south to the sea.
The spillway can accommodate about 1.87 million gallons of water per second, diverting it to the Gulf of Mexico by way of Lake Pontchartrain, and sparing the low-lying city of New Orleans from high waters. The spillway is scheduled to open Monday, the Corps said.
Earlier this week, the Corps of Engineers intentionally breached a levee south of where the Ohio River joins the Mississippi River to help alleviate water pressure on levees throughout the region.
The Corps said the breach would help lower river levels and prevent widespread flooding in communities such as Cairo, Illinois, which sits at the confluence of the two rivers.
CNN's Marlena Baldacci and Phil Gast contributed to this report.