The lagoon system is divided in two units (Razelm and Sinoe) formed by semi-independent lakes. Razelm has an area of 415km2 and a maximum depth of 3.2m and Sinoe has 171km2 and a maximum depth of 2.2m.
The lagoon shares its southern, western and eastern limits with the Danube Delta Biosphere Reserve boundaries, the northwestern limit being represented by transitional areas (ponds, marshes, wetlands and channels). The lagoon was almost closed from the sea in the 1970s, to be a strategic resource of freshwater. Nowadays, there is only one inlet, at Edighiol, that insures exchanges with the sea. Water level in the lagoon fluctuates with the Danube water level.
Due to its hydrology and morphology, Razelm-Sinoe behaves like a large, eutrophic lake. Eutrophication, also enhanced by inputs from agricultural activities inland, affects water quality, mainly in the spring and summer, leading to a decrease in fish stocks. Fishing is one of the traditional occupations in the region and traditional food is one of the main tourist attractions in villages bordering the lagoon along with ancient sites located in the west, fishing and boat trips all around the lagoon.
GeoEcoMar has been performing systematic water quality measurements beginning with 2010. So far, there is very little knowledge about the eutrophication phenomenon, its phenology and controlling factors in the Razelm lagoon and its effects on the ecosystem.