ABOARD THE DREDGE POTTER, on the Mississippi River — This ship is making sure that the Big River, shrinking under one of the worst droughts in modern history, stays deep enough.

The Potter is scooping this stretch of the Mississippi River’s navigation channel just south of St. Louis, the ship’s 32-foot-wide head sucking up about 60,000 cubic yards of sediment each day and depositing it via a long discharge pipe a thousand feet to the side in a violent, muddy plume that smells like muck and summer.

The Army Corps of Engineers has more than a dozen dredging vessels working the Mississippi this summer. Despite being fed by water flowing in from more than 40 percent of the United States, the river is feeling the ruinous drought affecting so much of the Midwest. Some stretches are nearing the record low-water levels experienced in 1988, when river traffic was suspended in several spots.

That is unlikely this year, because of careful engineering work to keep the largest inland marine system in the world passable. But tow operators are dealing with the shallower channel by hauling fewer barges, loading them lighter and running them more slowly, raising their costs. Since May, about 60 vessels have run aground in the lower Mississippi.