SIOUX CITY, Iowa — Record Big Sioux River flooding prompted residents in three states to hurriedly prepare for the rising water Thursday, with people lining up for sandbags and moving museum artifacts and other items to higher ground.
The fast-moving Big Sioux has been swollen by days of thunderstorms and is expected to crest Friday more than a foot above the previous record level set in 1969, threatening homes and businesses in Iowa, Nebraska, and South Dakota.
In North Sioux City, S.D., dozens of National Guard soldiers were rushing to fill sandbags for residents of the McCook Lake neighborhood, where up to 400 homes were in danger of flooding.
Residents including Ashley Caskey waited for hours in a line of pickup trucks that inched toward the sandbag-filling stations.
‘‘We are just happy to get sandbags at this point,’’ Caskey said.
Tim Webster, who lives in an upstairs apartment on McCook Lake, said he wasn’t worried about his place but was helping friends. ‘‘Anybody who knows me knows I’ve got a truck, so let’s do this,’’ he said.
This is the worst flooding the region has seen since 2011, when the Missouri River remained high for months, causing tributaries to back up and testing the levee system. The fact that the levee held for long at that time showed it’s effective, said Jade Dundas, assistant city manager for public works for Sioux City, Iowa.
This time, the Big Sioux should begin receding Saturday and stop flooding even nearby agricultural land by Monday morning.
‘‘This kind of a quick up and down does give us some sense of confidence,’’ Dundas said.
The city had to extend one of its levees by about 600 feet, and that work is finished. On Thursday, Sioux City crews helped property owners fill sandbags as a precautionary measure, he said.
At the Railroad Museum near the river in Sioux City, volunteers helped staff move artifacts to higher ground because the main building is expected to get about 5 feet of water, museum executive director Matt Merk said.