High water levels caused by heavy rain closed locks along the Mississippi River in Missouri that could slow down barge operators upriver in Minnesota trying to go south.

The Associated Press reports barges traveling north from St. Louis will likely be stalled while four locks from Clarksville to Canton remain closed and a fifth is expected to close Saturday.

The Army Corps of Engineers told Reuters that it's unclear how long the closures would last as more rain is expected in the Midwest over the next several days.

The corps says lock closures are essential in protecting critical components and facilities from flood waters.

The National Weather Service forecast Friday predicts the river will reach 39.7 feet in St. Louis by early next week, the Belleville News-Democrat reports. Rain expected Friday and Saturday could push levels to the 40 foot mark, which is considered to be major flood stage.

U.S. grain exporters rely on the Mississippi River and its tributaries to transport corn, soybeans, wheat and other farm products from production areas such as Iowa and Illinois to terminals near the Gulf of Mexico, Reuters said.

About 60 percent of all U.S. grain exports exit the country via the Gulf.