A cryptodepression is a depression in the Earth's surface that is below mean sea level, and which is filled by a lake. The term is derived from the Ancient Greek word κρύπτoς ('hidden') and depression. A cryptodepression is often due to creation of a rift valley or a glacial lake. Lakes are often long and narrow. Further, the surrounding landscape and the shore of the lake can be very steep.

Cryptodepression - Wikipedia