Lieutenant O'Neill, British consul at Mozambique, writing in 1880, fixed at about 3000 the number then annually exported from the coast between the rivers Rovuma and Zambesi.
The southern frontier goes direct from the last-named point eastward to the Rovuma river, which separates German and Portuguese territory.
A little before the Indian Ocean is reached the frontier is deflected south so as to leave the mouth of the Rovuma in German East Africa.
The largest streams are the Rovuma and Rufiji (q.v.), both rising in the central plateau and flowing to the Indian Ocean.
Formerly the lake seems to have found an outlet northwards to the Lujenda branch of the Rovuma, but with the sinking of its level it is now separated from the Lujenda by a wooded ridge some 30 to 40 ft.