The Razim–Sinoe lagoon complex is geologically and ecologically related to the delta proper; the combined territory is listed as a World Heritage Site.

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).

[6] 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 human clearing of forests in the Danube basin during the 1st and 2nd millennium.

[7]At present, the delta suffers from a large sediment deficit, after the construction of dams on the Danube and its tributaries in the later half of the 20th century.

(Saint George) Chilia, in the north, the longest, youngest, and most vigorous, with two secondary internal deltas and one microdelta in full process of formation at its mouth (to Ukraine).

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[clarification needed] in Europe, with numerous rare species.

Between the aquatic and terrestrial environments is interposed a swampy, easily flooded strip of original flora and fauna, with means of adaptation to water or land, depending on the season or hydrological regime.

At the contact between freshwater and sea water, some special physical, chemical and biological processes take place, which have led biologists to consider this area as a very different ecosystem called beforedelta.

Of the fish, the most important are Tench (Tinca tinca), common bream (Abramis brama), common rudd (Scardinius erythropthalmus), Prussian carp (Carassius auratus gibelio), wels catfish (Silurus glanis), European perch (Perca fluviatilis), and northern pike (Esox lucius).

The most important are the tufted duck (Aythya fuligula), red-crested pochard (Netta rufina), mallard (Anas platyrhynchos), greylag goose (Anser anser), pygmy cormorant (Microcarbo pygmeus), purple heron (Ardea purpurea), great white egret (Egretta alba), little egret (Egretta garzetta), Eurasian spoonbill(Platalea leucorodia), great white pelican (Pelecanus onocrotalus), Dalmatian pelican (Pelecanus crispus), mute swan (Cygnus olor), and glossy ibis (Plegadis falcinellus).

Among the mammals, there is the Eurasian otter (Lutra lutra), European mink (Mustela lutreola), little ermine (Mustela erminea aestiva), wild boar (Sus scrofa), and wild cat (Felis silvestris), in winter the European hare (Lepus europaeus) and, on the brink of disappearing from the delta, the wolf and the fox.

The East Asian raccoon dog (Nyctereutes procyonoides), bizam/introduced muskrat (Ondatra zibethica), and to some extent South American nutria (Myocastor coypus), are recent species that have successfully adapted.

On the levees of Letea and Caraorman, mixed forests of oaks (Quercus robur, and Quercus pedunculiflora) with various other trees (Fraxinus pallisiae, Ulmus foliaceae, Populus tremula), shrubs (Prunus spinosa, Crataegus monogyna, Rosa canina, and Berberis vulgaris, among others), and vines (Vitis sylvestris, Hedera helix, Humulus lupulus, Periploca graeca, which reaches up to 25m) grow on sand dune areas.

[12] Its acute isolation and harsh conditions of living, based mainly on subsistence, made the Danube Delta a place of emigration, or transit at least.

Very few of those born in the region stay there through adulthood; at the same time, the origins of its inhabitants vary widely, as people from many parts of Romania can be found in the delta.

Distinctive to the region, but very rare as an ethnic entity, are the Lipovans, descendants of the Orthodox Old Rite followers who fled from religious persecution in Russia during the 18th century.

The Treaty of Paris of 1856, which ended the Crimean War, assigned the Danube Delta to the Ottoman Empire and established an international commission which undertook a series of works to help navigation.

Natural environments have been altered, the breeding pattern of fish has been disrupted, and the flows in the main arms have increased, with serious consequences regarding the discharge of alluvia and the erosion of banks.

In 1991, agricultural land in the delta surpassed 100,000 hectares, and more than a third of its surface has been affected by crop cultivation, forest plantation, or pisciculture (fish farming).

In 2004, Ukraine inaugurated work on the Bistroe Channel that would provide an additional navigable link from the Black Sea to the populous Ukrainian section of the Danube Delta.