Caspian Sea
The wide and endorheic Caspian Sea has a north–south orientation and its main freshwater inflow, the Volga River, enters at the shallow north end. Two deep basins occupy its central and southern areas. These facts lead to horizontal differences in temperature, salinity, and ecology. The Caspian Sea spreads out over nearly 750 miles (1,200 km) from north to south, with an average width of 200 miles (320 km). It covers a region of around 149,200 square miles (386,400 square km)—bigger than the region of Japan—and its surface is about 90 feet (27 meters) below sea level. The sea bed in the southern part reaches as low as 1,023 m (3,356 ft) below sea level, which is the second lowest natural depression on earth after Lake Baikal (−1,180 m, −3,871 ft). The ancient inhabitants of its coast perceived the Caspian Sea as an ocean, probably because of its saltiness and large size.
Uzboy
At various times in the past one or more branches of the Oxus split off from the Oxus delta and flowed west into the fresh-water Sarykamysh Lake. This was drained south by the Uzboy River about 175 km to near Igdi where it turned and flowed about 290 km west, reaching the Caspian at Krasnovodsk Bay through the Bala-Ishem salt marshes. There was a large waterfall, a place called the Lion’s Jaw and at one point the river disappeared underground for some distance. (Glukhovskoy does not mention it, but GoogleEarth shows a dry river bed that starts about 100 miles west of the Oxus and runs about 400 miles west to join the Uzboy near Igdi.) All geographers, from the ancient Greeks to the early Arabs, reported that the Oxus flowed into the Caspian, although their accounts are vague. From the 10th to the 13th centuries there are no reports of a Caspian mouth. It is thought that a dam was built near the old capital of Konya-Urgench and that this dam was destroyed by the Mongols when they sacked the city in 1220. We again hear of a Caspian mouth from about 1310 to 1575. It is possible that the main current shifted from the Aral to the Caspian, causing the Caspian to rise and the Aral to sink. There may have been a significant population along the Uzboy and farmland in what were later the marshes at the north end of the Oxus delta. It seems that about 1575 the east branch of the Oxus cut through some hills causing the main current to shift to the Aral Sea. Also a dam was built near the old site to retain the remaining water and to deny it to the Turkomans who were in the habit of raiding the Oxus delta. This not only blocked the Uzboy but caused the Sarikamish to slowly dry up.