In the spring of 1927, relentless rains and northern melt caused the Mississippi to overflow its banks. More than 27,000 square miles of land from Illinois to Louisiana were submerged, and nearly one million people were left homeless. In 1928, the Federal Flood Control Act mandated permanent levees along the banks of the Atchafalaya Basin and both sides of the Mississippi River for more than 1,000 miles. Spillways were constructed upriver for New Orleans, where excess water could be dumped into Lake Ponchartrain. These safety measures continue to protect southern Louisiana from yearly floods and prevent a repeat of the catastrophe of 1927.