Deputies warned people Sunday to get out as water gushing from a floodgate for the first time in four decades crept ever closer to communities in the Louisiana Cajun country, slowly filling a river basin like a giant bathtub.

Most residents heeded the warnings and headed for higher ground, even in places where there hasn't been so much as a trickle, hopeful that the flooding engineered to protect New Orleans and Baton Rouge would be merciful to their way of life.

Days ago, many of the towns known for their Cajun culture and drawling dialect fluttered with activity as people filled sandbags and cleared out belongings. By Sunday, some areas were virtually empty as the water from the Mississippi River, swollen by snowmelt and heavy rains, slowly rolled across the Atchafalaya River basin. The floodwaters could reach depths of 20 feet in the coming weeks.

The spillway's opening diverted water from heavily populated New Orleans and Baton Rouge — along with chemical plants and oil refineries along the Mississippi's lower reaches — easing pressure on the levees there in the hope of avoiding potentially catastrophic floods.