Kayes is the limit of navigability from the sea.
Since 1842, but more especially since 1871, improvements have been made in the navigability of the Elbe by all the states which border upon its banks.
Navigability really only begins again at Gondokoro on the Sudan frontier, from which point steamers ply to Khartum (see Nile).
The Russian navigator Nevelskoi in 1849 definitively established the existence and navigability of this strait.
The Beni and its great affluent, the Madre de Dios, though of smaller volume and extent than the Mamore, are of much greater economic importance, owing to their navigability, the fertility of the region they drain, and the great forests along their banks.
The importance of Gondokoro lies in the fact that it is within a few miles of the limit of navigability of the Nile from Khartum up stream.