Slidell, Louisiana (CNN) -- Authorities dropped a mandatory evacuation order Sunday for neighborhoods threatened by a strained lock on a southeast Louisiana canal, but still recommended people stay away.
"As there is still a potential threat, even though reduced, a voluntary evacuation remains in place until the Army Corps of Engineers deems the lock stable and safe," the president and sheriff of St. Tammany Parish announced late Sunday morning. "Please stay vigilant."
The lock authorities feared would fail was on a man-made canal that juts off the Pearl River, near the Mississippi state line. The river has been swollen by rain from last week's Hurricane Isaac, forcing authorities to relieve pressure on the structure by releasing water Saturday and Sunday.
Earlier Sunday, St. Tammany Parish President Pat Brister told CNN the water level at the lock has been reduced "tremendously" since Saturday night, and "We feel a lot better."
But the waters were still rising Sunday afternoon. Christina Garcia stopped by a boat ramp around the corner from her home periodically, counting off heel-to-toe steps from the waterline to the top to track the river's rise.
"When I first started, it was like, 14, and now I'm down to probably 10," Garcia said. The river "is starting to come up slowly, but there is some concern. We are trying to take all precautions."
Forecasters predict the Pearl River will crest Monday at 19.5 feet, more than five feet above flood stage. That will result in "major flooding" of at least two subdivisions near the banks and threaten areas in the southeastern corner of the parish, according to the National Weather Service.
U.S. Homeland Security Secretary Janet Napolitano visited the parish on Sunday, during a trip that also included stops in Mississippi where she met with that state's governor and other officials.
President Barack Obama will be in Louisiana on Monday for a briefing with local officials and to tour flood-damaged areas in St. John the Baptist parish.
What's left of Isaac, meanwhile, soaked in and around the Ohio River valley on Sunday, bringing stormy weather from Nashville, Tennessee, to Indianapolis.
The storm's remnants have brought much-needed rain to parts of the lower Midwest. But the system skirted most of the Midwestern and Plains states where this year's drought -- which the National Climatic Data Center reported last month was affecting a majority of the U.S. mainland, the most since 1956 -- has been most devastating.
"Certainly, it helped some locations in our far eastern counties in Oklahoma, but there was very little beneficial rain," said Pete Snyder, a National Weather Service meteorologist in Tulsa.
Nearly all of Oklahoma, Arkansas, Missouri, Iowa, Nebraska and Kansas fall under the worst two drought categories. Isaac dumped heavy rain across southern Arkansas last week, with some flooding reported around Little Rock and Pine Bluff. But the northwestern city of Fayetteville, which is nearly 11 inches below its normal rainfall totals for the year, got just over an inch, Snyder said.
Flood warnings remained posted for parts of two northeastern Arkansas counties along the Cache River on Sunday. Parts of Missouri and Illinois saw up to six inches of rain Saturday, and the National Weather Service issued a flood warning Sunday for parts of southern Illinois.
Isaac is blamed for at least 19 deaths in Haiti and at least four more in Louisiana and Mississippi after making landfall last week as a Category 1 hurricane -- on the seventh anniversary of Hurricane Katrina -- near the mouth of the Mississippi River.
The storm posed the first real test to New Orleans following a $14.5 billion federal effort to reconstruct the city's flood control system after it failed during Katrina in 2005. Katrina killed nearly 1,800 people, most when the storm overwhelmed the levee system and flooded the city.
Though much weaker than Katrina when it came ashore, Isaac moved slowly and dumped enormous amounts of rain on Louisiana and Missouri. In Plaquemines Parish, near the mouth of the Mississippi River, homes and businesses flooded after a parish-maintained back levee failed. Officials were intentionally breaching levees in strategic areas in the parish, in hopes of getting "the bulk of this water out in five to seven days," Plaquemines Parish President Billy Nungesser said Saturday.
Hundreds of thousands in the region were without power early Sunday, including at least 320,000 Entergy Louisiana customers, officials said
Residents began returning home over the weekend in Helena, Mississippi, where National Guard troops rescued hundreds trapped by rising waters brought on by Isaac. Annie Judge returned home Saturday to find more than four feet of water inside her home.
"Clothes, my laptop, a bunch of baby stuff, pictures," all ruined, she told CNN affiliate WLOX. "All the furniture is ruined."
CNN's Greg Botelho, Chelsea J. Carter, Matt Smith and David Ariosto contributed to this report.