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— A rare winter flood shut down portions of two interstates on Tuesday, threatened hundreds of homes and caused sewage to flow unfiltered into waterways.

Torrential rains over the past several days pushed already swollen rivers and streams to virtually unheard-of heights in parts of Missouri and Illinois. Record flooding was projected at some Mississippi River towns, and the Meramec River near St. Louis was expected to get to more than 3 feet above the previous record by late this week.

At least 18 deaths in Missouri and Illinois are blamed on flooding, mostly involving vehicles that drove onto swamped roadways.

The river on Tuesday spilled over the top of the levee at West Alton, Missouri, about 20 miles north of St. Louis. Mayor William Richter ordered any of the town’s approximate 520 residents who had not already evacuated to get out of harm’s way.

Missouri Gov. Jay Nixon activated the National Guard to assist with security in evacuated areas and to help divert traffic at road closure sites.

The U.S. Army Corps of Engineers said Tuesday that the rising Mississippi and its tributaries were threatening to overtop 19 federal levees in the St. Louis area. The threatened areas include Perry and Ste. Genevieve counties in Missouri, and Randolph County in Illinois. The levee protecting the historic downtown of Ste. Genevieve is not believed to be threatened.

In another eastern Missouri town, Union, water from the normally docile Bourbeuse River reached the roofs of a McDonald’s, QuikTrip and several other businesses. The river reached an all-time high Tuesday, nearly 20 feet above flood stage.

Interstate 44 was closed near the central Missouri town of Rolla, and a section of Interstate 70 was shut down in southern Illinois. Hundreds of smaller roads and highways were also closed across the two states, and flood warnings were in effect.

In St. Louis, more than 100 volunteers turned out in blustery, cold conditions to fill sandbags where a flooded waterway threatened hundreds of homes.

The River Des Peres is a man-made storm sewer channel that flows through south St. Louis into the Mississippi River, a few miles south of the Anheuser-Busch brewery. The channel is deep enough that flooding isn’t a concern under normal conditions.

But there is nothing normal about this December flood.

The Mississippi River is expected to reach nearly 15 feet above flood stage on Thursday at St. Louis, which would be the second-worst flood on record, behind only the devastating 1993 flood.

Maureen Hooch, 57, was among the volunteers at that 1993 flood, and she was out again Tuesday.

“The last time I was out here it was 1,000 degrees,” Hooch recalled. “They had a bus you could get on to cool off. I prefer the cold.”

Alderman Larry Arnowitz said up to 500 homes could be threatened if the River Des Peres rises much more than projected.

But Lisa Muxo, 45, said her basement was already taking on water.

“These are our neighbors, our friends,” said Muxo, who brought her teenage son and three of his friends to help sandbag. “We need to help each other.”

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