Significant portions of the United States remained under flood warnings on Wednesday morning as the fallout from a powerful storm system left their communities waterlogged.

The National Weather Service issued flood warnings in at least 18 states in the Gulf Coast, Atlantic Coast and Ohio Valley. Most of the warnings were concentrated in Illinois, Missouri and Oklahoma, three of the states that received the highest rainfall totals during the recent storm.

According to the National Weather Service, the storm dropped six to 12 inches of rain across those three states and northwest Arkansas, where additional flood warnings were in effect.

The National Oceanic and Atmospheric Administration (NOAA) said 379 river gauges across the country were in flood stage Wednesday morning, including 48 that reported “major flooding.” Those were down from Tuesday’s respective totals of 438 and 53, but that decline likely provided little relief to the regions that were still underwater, or where floodwaters were expected to rise.

Those river gauges don’t necessarily include lakes or other smaller bodies of water, like creeks or streams, that were also flooding. The rivers alone reached historic levels in several communities.

According to the NOAA, the Meramec River, which runs just south of Saint Louis, had already surpassed its record crests in two different locations on Wednesday morning. That included a whopping 45.33-foot total near Eureka, which was about 2.5 feet above a 33-year-old record and more than 25 feet above the threshold for what the NOAA considers to be major flooding. The waters were expected to continue to rise, reaching an all-time high of 46.2 feet later Wednesday.

Those rising waters were also forcing some mandatory evacuations and road closures.

City officials in Valley Park, Missouri, ordered residents to leave their homes and seek higher ground as the Meramec River reached 40 feet, according to the city’s Facebook page. The Missouri Department of Transportation shut down a 20-mile stretch of Interstate 44 near St. Louis because of flooding, according to a news release. That road is expected to be closed several days.

The National Weather Service reported that Union, Missouri, received more than a foot of rain in the storm. According to the NOAA, the Bourbeuse River reached a historic height of 34.31 feet on Tuesday before receding to 29.3 feet on Wednesday morning. Still, that was three feet above the threshold for major flooding in the city, located some 55 miles southwest of Saint Louis.

Missouri Governor Jay Nixon has declared a state of emergency and activated the National Guard, according to a news release from his office. The National Guard will assist evacuation efforts, as well as ensure traffic stays away from the numerous closed roads. Floods have killed 13 people in the state alone, according to the governor’s office, 12 of whom died when rushing waters swept vehicles off roads. St. Louis County officials also declared a countywide state of emergency, writing in a news release that the waters trapped people in businesses and homes.

Some locations along the Mississippi River were also expected to see record flooding, according to the NOAA. But even in areas where records weren’t broken, the waters were still very high.

The NOAA indicated there was major flooding along several rivers in Illinois, Missouri, Texas, Oklahoma and Arkansas. Minor or moderate flooding was occurring in parts of the southeast.