After the Coosa and Tallapoosa rivers, the principal tributary of the Alabama is the Cahaba River, which is about long and joins the Alabama River about below Selma. The Alabama River's main tributary, the Coosa River, crosses the mineral region of Alabama and is navigable for light-draft boats from Rome, Georgia, to about above Wetumpka (about below Rome and below Greensport), and from Wetumpka to its junction with the Tallapoosa. The channel of the river has been considerably improved by the federal government.