The Danube Delta is the second largest delta in Europe, after the Volga Delta, and is the best preserved on the continent. The greater part of the Danube Delta lies in Romania (Tulcea county), while its northern part, on the left bank of the Chilia arm, is situated in Ukraine.

The approximate surface is 4152 km², of which 3446 km² are in Romania. If the lagoons of Razim-Sinoe (1015 km² of which 865 km² water surface; situated in the south, but attached to the Danube Delta from geological and ecological perspecives, as well as being the combined territory of the World Heritage Site) are to be added, the considered area of the Danube Delta grows to 5165 km².