The country is well watered, but with the exception of the Rufiji the rivers, save for a few miles from their mouths, are unnavigable.
The largest streams are the Rovuma and Rufiji (q.v.), both rising in the central plateau and flowing to the Indian Ocean.
They are spread over the central plains, and have for neighbours on the south-east, between Nyasa and the Rufiji, the warlike Wahehe.
In the delta of the Rufiji and in the Kilwa district cotton-growing was begun in 1901.
The Rovuma, Rufiji, Tana, Juba and Webi Shebeli principally drain the outer slopes of the East African highlands, the last named losing itself in the sands in close proximity to the sea.