Quercus nigra is a medium-sized deciduous tree, growing up to 30 meters (98 feet) tall with a trunk up to 1 m (3 ft 3 in) in diameter.

The acorns are arranged singly or in pairs, 10–14 millimeters (3⁄8–1⁄2 in) long and broad, with a shallow cupule; they mature about 18 months after pollination in autumn of the second year.

It is adapted to wet, swampy areas, such as along ponds and stream banks, but can also tolerate well-drained sites and even heavy, compacted soils.

Water oak is frequently used to restore bottomland hardwood forests on land that was previously cleared for agriculture or pine plantations.

Water oak acorns are an important food for white-tailed deer, eastern gray squirrel, raccoon, wild turkey, mallard, wood duck, and bobwhite quail.