Natural vegetation along the river is composed primarily of two major plant communities, the floodplain forest of willow and cottonwood, and the elm and oak woodland typical of the bluffs that border the floodplain in Nebraska.
Varying stages of floodplain vegetative succession are evident throughout the park. On the sandbars and newly deposited accretion land adjacent to the riverbanks grow the pioneer species of floodplain succession: annual weeds, short-lived grasses, sedges, and seedling willow and cottonwood. Farther back and higher above the water table, larger willow and cottonwood trees dominate until finally a floodplain forest of cottonwoods occurs on the highest banks and islands. The understory in the mature cottonwood forest is primarily dogwood, sumac, wild grape, and poison ivy.
The sparse vegetation under the mature cottonwoods consists mostly of scouring rush, Kentucky bluegrass, smooth brome, and other invasive grasses and weeds.
In contrast to mixed floodplain forest and agricultural use on the floodplain are the hardwood forests of the adjoining bluffs. The slopes support a dense growth of oak, ash, mulberry, and walnut, with burr oak as the dominant species.
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