Freshwater and salt water come together in the coastal lagoons of the delta, creating an environment of highly singular characteristics.

The Ebro delta, in the extreme south east of Catalonia, has an extension of approximately 350 km². This space is a protected nature park as it is a singular habitat not only for marine organisms, but also for the numerous migratory sea birds that generally settle in there temporarily.

It is an intermediate step between freshwater (from the river Ebro) and sea water, so that the first, ongoing out into the sea, gradually mixes with the second, thus reducing the salinity. This creates a series of intermediate, fluctuating saline environments that does not facilitate the life of the different organisms that live there.The different species that live there can withstand relatively high falls and rises in the salinity, thanks to an effective regulation of the internal fluids. However, there are species that not only remain in the transition area (or water mixture), but insert completely in one water or the other. These are species that carry out the so-called migrations, such as the eel for instance (Anguilla anguilla).

Eel (Anguilla anguilla) 

Beluga sturgeon (Huso huso) 

Other common marine organisms that can be found in this community:

• Thicklip grey mullet (Chelon labrosus)
• Siberian sturgeon (Acipenser baeri)