Alabama’s longest free flowing river, the Cahaba is approximately 194 miles long with two distinct biological areas – above the fall line (upper Cahaba River) and below the fall line (lower Cahaba River). The headwaters form in St Clair County. The river flows through the Alabama Valley and Ridge and meets the East Coast Gulf Coastal Plain near Centreville at the fall line. The area in Jefferson County is characterized by Ecoregion 67h – Southern Sandstone ridges of the Southwestern Appalachians.
The Cahaba has two personalities in the Centreville region. Above the park lies the Cahaba River National Wildlife Refuge, whose access to the river provides swimming, paddling, a lot of nature studies through the Cahaba River Society and close-up views of the famous Cahaba lilies when they bloom in May and June. But no camping is allowed here. The river on the Refuge runs excitedly down the fall line over drop after drop and shoal after shoal for miles. The fall line is essentially a ramp that runs off the stone substrata under the state’s northern geology and sends our rivers meandering aimlessly through the coastal plain above the Gulf. Centreville’s park is at the very toe of the fall line, and the river wanders through farmland bottoms with ample sandbars left and right all the way to its terminus at its confluence with the Alabama River below Selma.- Alabama Scenic River Trail, Jim Felder.