The waters of the Mississippi River below the Stone Arch Bridge in Minneapolis were low enough Monday for passersby to wander the river bottom.

The U.S. Army Corps of Engineers is slowly lowering river levels by 12 feet to inspect the upper and lower locks and dams at St. Anthony Falls. Engineers opened the dam gates and began drawing down this section of the river on Saturday.

The river will reach the target water level on Tuesday and remain there for two days as engineers inspect the locks for the first time since 2015, according to the agency.

River levels upstream of Upper St. Anthony Falls are not affected. The river will gradually return to normal levels after the inspections.

The inspections are meant to ensure the locks and surrounding structures are sound and can safely operate. Corps officials may identify areas that require further review and maintenance, allowing them to request and receive funds to address needs before problems arise.

The Upper St. Anthony Falls lock and dam was constructed in 1963. The upper lock closed to navigation in 2015 but is occasionally used to reduce flood risk.

Want to catch a rare glimpse of what the river looked like before the lock and dam? The Upper St. Anthony Falls lock and dam will be open to the public on Tuesday, Wednesday and Thursday from 10 a.m. to 4 p.m. Park rangers and volunteers will be on hand to answer questions.