Caspian Sea
The Caspian Sea, like the Black Sea, Namak Lake, and Lake Urmia, is a remnant of the ancient Paratethys Sea. It became landlocked about 5.5 million years ago due to tectonic uplift and a fall in sea level. During warm and dry climatic periods, the landlocked sea almost dried up, depositing evaporitic sediments like halite that were covered by wind-blown deposits and were sealed off as an evaporite sink when cool, wet climates refilled the basin. (Comparable evaporite beds underlie the Mediterranean.) Due to the current inflow of fresh water, the Caspian Sea is a freshwater lake in its northern portions, and is most saline on the Iranian shore, where the catchment basin contributes little flow. Currently, the mean salinity of the Caspian is one third that of Earth's oceans. The Garabogazköl embayment, which dried up when water flow from the main body of the Caspian was blocked in the 1980s but has since been restored, routinely exceeds oceanic salinity by a factor of 10.
Kura (Caspian Sea)
Steppe characterizes the arid reaches of the Kura River catchment, while meadows are often found in the alpine areas. The Kura River area is considered as part of the Kura-South Caspian Sea Drainages ecoregion. Some portions of the river flow through a semi-desert environment. Forest cover is sparse. Almost 60 species of fish inhabit the Kura River and its tributaries. Some common families include loach, bleak, trout and nase, and many of these fish are endemic to the region. Among rivers of the Caucasus, the Kura has the largest number of endemic species. The upper section of the river supports much more biodiversity than the lower half, which is typically more turbid and polluted. This pattern is also apparent in most of its tributaries, especially the larger ones that span more climate zones, such as the Aras and Alazani. There are many lakes and wetlands along the Kura's lower course, most of which are formed by flooding, and some of which are formed by irrigation runoff water. Many lakes also form at the mouths of small tributaries that do not reach the ultimate destination in the Caspian most of the time. The local name for these lakes translates to "dead lake" or "dead water", suggesting that these lakes do not support much biodiversity.