At Memphis (map), Tennessee, the Mississippi crested late Monday at 47.8 feet (14.5 meters)—less than a foot below the city's record, set in 1937.

With the river now receding in the city and the rest of Shelby County, nature has "put the pin back in the grenade," said county spokesperson Steve Shular.

But explosive animal encounters may await returning evacuees.

"We're starting to see some issues, especially with the snakes," Shular explained. "We've definitely seen a lot of snakes, like water moccasins"—venomous pit vipers with potentially fatal bites that are also called cottonmouths (water moccasin picture).

With swollen rivers reaching up near homes and neighborhoods, "we want to make sure people understand that the rules have changed," Shular said.

"When