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.
Caspian lowland desert
The Caspian lowland desert ecoregion (WWF ID:PA1308) is an ecoregion that covers the north and southeast coasts of the Caspian Sea, including the deltas of the Volga River and Ural River in the northern region. While the region gets relatively low amounts of precipitation (less than 200 mm/year), wildlife is supported by the river estuaries and the sea itself. The wetlands are an internationally important area for bird nesting and migratory resting. The ecoregion is in the Palearctic ecozone, and the Deserts and Xeric Shrublands biome. It has an area of .