The Tharthar depression was formed during the Holocene age, mainly by karstification, due to dissolving of gypsum rocks of the Fatha Formation nearby.

[2] Tharthar covers roughly 2,050 km2 (790 sq mi) and flows from the central and eastern parts of the Sinjar Mountains and adjacent hills, with a floor of –3m above sea level.

Tharthar Lake is considered the main wintering grounds for many threatened species of migrant birds such as saker falcon, MacQueen's bustard, and sociable lapwing.

All these near threatened species were recorded on passage and the endemic race of hooded crow [Corvus cornix capellanus] was present.

Ten fish species have been found in the lake including: Aspius vorax, yellowfin barbel, B. luteus, B. sharpeyi, goldfish , Cyprnion kais, common carp, Silurus triostegus, Chondrostoma regium, and Liza abu.