The modern Danube Delta began forming after 4,000 B.C. in a gulf of the Black Sea, when the sea rose to its present level. A sandy barrier blocked the Danube gulf where the river initially built its delta. Upon filling the gulf with sediments, the delta advanced outside the barrier-blocked estuary after 3,500 B.C. building several successive lobes[2][3]: the St. George I (3,500-1,600 B.C.), the Sulina (1,600-0 B.C.), the St. George II (0 B.C.-Present) and the Chilia or Kilia (1600 A.D.-Present).

The Danube Delta is a low alluvial plain, mostly covered by wetlands and water. It consists of an intricate pattern of marshes, channels, streamlets and lakes. The average altitude is 0.52 m, with 20% of the territory below sea level, and more than half not exceeding one meter in altitude. Dunes on the most extensive strandplains of the delta (Letea and Caraorman strandplains) stand higher (12.4 m and 7 m respectively). The largest lakes are Dranov (21.7 km²), Roşu (14.5 km²), Gorgova (13.8 km²).

The Danube Delta falls within east European steppe ecosystem, with Mediterranean influences. As a young region in full process of consolidation, the Danube Delta represents a very favourable place for the development of highly diverse flora and fauna, unique in Europe, with numerous rare species. It hosts 23 natural ecosystems, but due to the extent of wetlands the aquatic environment is prevalent; the terrestrial environment is also present on the higher grounds of the continental levees, where xerophile ecosystems have developed. Between the aquatic and terrestrial environments, is interposed a swampy, easily flooded strip of original flora and fauna, with means of adaptation for water or land, depending on the season or the hydrological regime. At the contact between freshwater and sea water, some special physical, chemical and biological processes take place, which determined biologists to consider this area as a very different ecosystem called beforedelta. Musura Gulf, north of Sulina, and Saint George Gulf are considered the most representative for this type of ecosystem.

Situated on major migratory routes, and providing adequate conditions for nesting and hatching, the Danube Delta is a magnet for birds from six major eco-regions of the world, including the Mongolian, Arctic and Siberian. There are over 320 species of birds found in the delta during summer,[4] of which 166 are hatching species and 159 are migratory. Over one million individuals (swans, wild ducks, bald coots, etc.) winter here.

The Danube Delta is perhaps the least inhabited region of temperate Europe. In the Romanian side live about 15,000 people, of which 4,600 in the port of Sulina, which gives an average density of approx. 2 inhabitants per km². The rest is scattered in 27 villages, of which only three, all situated marginally, have more than 500 people (2002). The town of Tulcea, at the western edge of the delta, but not included in it, has a population of 92,000 (2002). It represents the node of the region and the gate to the delta. The acute isolation and the harsh conditions of living, based mainly on subsistence, made the Danube Delta a place of emigration, or at least of transit. Very few of the people born here stay through adulthood; at the same time, the origins of the inhabitants fall within a wide range, as people from the most various places of Romania can be found in the delta. The total population has somewhat remained constant throughout the 20th century; there were 12,000 inhabitants in the 1890s, and 14,000 before the Second World War. Romanians count for approximately 80%, and Ukrainians for 10%. Other people living in the delta include Greeks, Turks and Bulgarians (1992). Distinctive for the region, but very vague as an ethnic entity are the Lipovans, descendants of the Orthodox Old Rite followers who fled Russia in the 18th century from religious persecution. About a third of the employed population is engaged in fishing and pisciculture, while another third is engaged in farming (1996). However, the quasi-totality practice fishing, more or less legally, as a means of subsistence or extra money.

The Ukrainian part of the delta is very well populated compared to the Romanian one. The town of Izmail has a population of 85,000, and Vilkovo, the main center of Lipovan community, 11,000 (2001).

Sources : Wikipedia