The high Ethiopian massif gives rise to a large number of waterways, including all the major rivers of this part of Africa. Some of the waters tend east towards the Indian Ocean, others descend west towards the Nile and then towards the Mediterranean; still others turn to Ethiopia or S. and are dispersed in the sands or end up in lake basins, without communication with the sea. The rivers of the Somali plateau belong to the Indian Ocean basin, which all originate in Ethiopian territory and flow into the sea (or are lost) in Italian Somalia: they are the Uabi or Uebi Scebeli with its tributaries and the three rivers, Web, Ganale and Daua, from whose confluence the Juba originates. The following belong to the Nile basin: 1. the Mareb (see gasc′), Which briefly marks the border between Ethiopia and Eritrea; 2. Takkazè, which originates in the Abuna Iosef group on the eastern edge of the Amhara plateau, and drains directly or through its tributaries the highest mountain ranges of Ethiopia: the Semien, M. di Macallè and of Adigrat (Torrente Geva) and the basin of Adua (Torrente Weri) forming a large arc of a convex circle to the North.: with the name of Setit it marks for a stretch the border with Eritrea. Takkazè and Mareb are tributaries of the Atbara (v.), Which originates with different branches (one of which is the Angareb) in the M. dei Wollo Galla, on the western edge of the plateau, and after a short journey it enters Sudanese territory at Gallabat: the average annual flow rate is 11,300 million cubic meters. 4. the Abai (Abbāy) or Blue Nile (see abai) originates from the southern end of Lake Tana, with an average flow rate of 3600 million cubic meters. per year: it turns first to the SE., then, with a grandiose curve, to the SW., and finally to the NW., separating the Goggiam from the Scioa and receiving numerous mountain tributaries from the two sides, including the Didessa (Ḍiḍḍēssā) which was born in the M. del Guma. The Abai leaves the Ethiopian territory near Fazogli (v. Nilo): its average annual flow in Sudan is 47.900 million cubic meters. The Sobat, a tributary of the White Nile, also originates from the western slopes of the galla plateaus: of its main branches, the Birbir originates in the Walleggà, the Baro originates in the Caffa mountains and crosses Gambela, while the Akobo flows from the Monti dei Magi and marks the border between Ethiopia and Sudan for a good distance. For Ethiopia 2007, please check extrareference.com.
The watercourses of the eastern and southern internal basins increase in importance from N. to S., due to the increasing rainfall and the greater extent of the floods. They are 1. the Kalkal, which descends from the mountains of Adigrat to the Endeli and with this marks a stretch of the Eritrean border; 2. Erebti and Dergaha, which from Macallè and Amba Alagi turn together towards the Piano del Sale (Alel bad); 3. the Golima, which is born in the Abuna Iosef group, not far from the sources of Takkazè, and gets lost in the danakil depression; 4. the Hawash, which originates in SO. of Addis Abeba and drains the slopes of the Scioa and those of the Guraghie with the numerous tributaries of its upper course: after a stretch of about 150 km. in the direction of SE., turns abruptly to NE., marrying the direction of the great sinking pit and running into the a large depression between the Itu Galla escarpment and that of Ancober: it dies in the Aussa, near the border of French Somalia, after having lost all its waters due to evaporation and lack of new food. The following flows into Lake Zuai (Dembel; 1846 m): 5. the Mukki, which descends from the Guraghie Mountains; 6. the Katara, coming from the Cilalo and Galamo families; Lake Hora communicates with the previous one but has salty waters; Lake Sciala or Lamina (1567 m.), also salty, is fed by small streams; the Regina Margherita lake (Abbaya; 1285 m) and the Ciamo lake (1050 m) which communicates with it, receive from N.: 7. the Bilattè; 8. the Ghidabo, and both have fresh water. Lake Stefania (m. 518), brackish, receives from N.: 9. the Galana Sagan, which originates from the mountains of the Amhara Burgi. But the course of the most important water of this southern sector is the Omo: 10. The Omo begins in the depression between the southern slopes of Scioa and the northern ones of Leka (Lieqā) and Ennarea, and immediately receives the waters of the slopes from S. western Guraghie; it then runs for a good stretch in a N.-S. direction, receiving the Gibè (Gibē) and the Gogeb from the W; then it deviates to the SW, then again to S. until it flows into a vast marshy delta at the northern end of Lake Rodolfo (407 m).
We have thus recalled all the main Galla lakes; these align strictly from NNE. to SSO. in the region between the escarpment of the two plateaus, which face each other, between the 8th and 5th lat. N. Lake Rodolfo, which is found with its northernmost point on this same alignment, however, has a N.-S direction; it is, moreover, almost entirely outside the Ethiopian territory. A few other lakes now remain to be remembered: in the middle of the Abyssinian plateau, between the Amhara and the Goggiam, is the most important of all, Lake Tana (1760 m). Almost piriform, this one measures about 70 km. in diameter and 3000 sq. km. of area, and has a variable depth between 30 and 70 m. and a total capacity of 14,550 million cubic meters. Its origin is due to the damming of the valley by a large lava flow, and it would be relatively recent (about 5000-10,000 years). There are two islands: Dek (Dag) and Degà Istefanos (Daqqa Estēfānos). The greenish water due to the copious content of diatoms and debris deriving from the vegetation of papyrus and herbs that clutter the banks, is very pure and perfectly tasteless (v.den). The main entrances are the Gumara and the Reb, from Ethiopia; the Abai is the only emissary (see Nile). Lake Ascianghi (Ašāngi) in the Amhara and lakes Haik (Ḥayq) and Ardibbo near Dessiè are of little importance. Mention has already been made of the salt ponds of Danakil (Alel Bad -120 m., Afreda -140 m.); for Lake Assal v. this voice.