Danube
"Danube" is an Old European river name derived from a Proto-Indo-European "*dānu". Other river names from the same root include the Dunaj, Dzvina/Daugava, Don, Donets, Dnieper, Dniestr, Dysna, Tana and Tuoni. In Rigvedic Sanskrit, "dānu" means "fluid, drop", in Avestan, the same word means "river". In the Rigveda, "Dānu" once appears as the mother of Vrtra, "a dragon blocking the course of the rivers." The Finnish word for Danube is Tonava, which is most likely derived from the word for the river in Swedish and German, "Donau". Its Sámi name "Deatnu" means "Great River". It is possible that "dānu" in Scythian as in Avestan was a generic word for "river": "Dnieper" and "Dniestr", from "Danapris" and "Danastius", are presumed to continue Scythian "*dānu apara" "far river" and "*dānu nazdya-" "near river", respectively.
Danube Delta
The modern Danube Delta began to form after 4000 BCE in a bay of the Black Sea, when the sea rose to its present level. A sandy barrier blocked the Danube bay where the river initially built its delta. Upon filling the bay with sediment, the delta advanced outside this barrier-blocked estuary after 3500 BCE, building several successive lobes: the St. George I (3500–1600 BCE), the Sulina (1600–0 BCE), the St. George II (0 BC–present) and the Chilia or Kilia (1600 CE–present). Several other internal lobes were constructed in the lakes and lagoons bordering the Danube Delta to the north (Chilia I and II) and toward the south (Dunavatz). Much of the alluvium in the delta and major expansion of its surface area in the form of lobes resulted from soil erosion associated with the clearing of forests in the Danube basin during the 1st and 2nd millennium. Geologist Liviu Giosan told "The New York Times":