The Don rises in Lake Ivan-Ozero, which has also an outlet to the Aka on the Central Russian elevation of ground. Its valley is at first deeply cut, its bed rocky. Then the valley widens and becomes symmetrical, the left bank becomes flat and swampy, covered in places by wide areas of sand. In the source region the direction of the river is south as far as Korotniak, then the river turns to the southeast, forms a sharp bend at the mouth of the Ilovla, approaching to within 60 km. of the Volga. Then the Don repeats on a small scale the direction of the course of the Dnieper, turns toward the southwest, and disembogues [83]in thirty arms, of which only three are navigable and only one accessible to sea-vessels, into the Sea of Azof. Its delta region is very rich in fish and is growing very rapidly. The general volume of the Don is twice as small as that of the Dnieper and is subject to many vacillations. During the spring floods the water-level reaches 6–7 m. above the normal and the river becomes as much as 10 km. wide. At the time of low-water, on the other hand, the river, despite its width (in the lower part of its course) of 200 to 400 m. and depths of 2–16 m., is full of sandbanks and shallows, so that navigation on the Don is but slightly developed, altho more than 1300 km. of its course may be considered fit for floating rafts of logs and 300 km. for ships. The freezing-time lasts on the average 100 days. Of the left-hand tributaries of the Don, the Voronizh, Bitiuh, Khoper, Medveditza, and the Manich (famous, because of its bifurcation) are the most important. Of the right-hand tributaries only one, the Donetz, is important. Its entire course belongs to Ukrainian national territory. It is 1000 km. long, and, in its southerly and then south-easterly direction, entirely analogous to the Dnieper and the Don. The Donetz flows in a broad valley and washes beautiful white cliffs along the steep right bank, crowned with dark forests. The Donetz is capable of floating rafts along a stretch of over 300 km., and is navigable for 200 km. more. Of the steppe-rivers which tend toward the Sea of Azof from the east, only the Yeia reaches its goal. All the rest end their courses in lagoons.