Ancient lake

Twelve of the 20 ancient lakes have existed for more than 2.6 million years[citation needed], the full Quaternary period.

In ancient times it was indisputably a true lake, but today it is saline and directly connected to the sea, leading many to consider it a large lagoon or bay.

Factors that influence the water level decreasing include fluvial-lacustrine sediment build-up, evaporation, natural drainage, and geophysical processes.

The location of the graben above the active rift zone results in a lake bottom that is constantly dropping in-depth and walls increasing in height.

Evolutionary characteristics including sexual selection, adaptive radiation and punctuated equilibrium are studied in ancient lakes due to their prolonged existence and general geographic isolation.

Lake Zaysan in Kazakhstan is one of the oldest lakes in the world.