The Nature Reserve was established in 1976, covering an area of 14,192 hectares (35,070 acres), characterized by an extensive surface of estuarine waters, vast fields intersected by creeks, marshes, salt flats and alluvial agricultural land (marshlands).

Around the estuary a saltmarsh has developed which is a zone of high productivity of polychaetes, molluscs and crustaceans, is an important breeding area for various fish species.

The many other species present attest to the biological richness and value for nature conservation in this region: the greater flamingo (Phoenicopterus roseus), greylag goose (Anser anser), the dunlin (Calidris alpina), black-tailed godwit (Limosa limosa), hen harrier (Circus cyaneus), osprey (Pandion haliaetus), bluethroat (Luscina svecica), common firecrest (Regulus ignicapillus) and Eurasian penduline tit (Remiz pendulinus).

[citation needed] In the wetlands around the estuary nesting birds include red-crested pochard (Netta rufina), little bittern (Ixobrychus minutus), little egret (Egretta garzetta) and purple heron (Ardea purpurea), marsh harrier (Circus aeruginosus], Montagu's harrier (Circus pyagurgus), black-winged stilt (Himantopus himantopus), collared pratincole (Glareola pratincola) and little tern (Sternula albifrons).

Other migrants which may be seen include Eurasian spoonbill (Platalea alba), Mediterranean gull (Larus melanocephalus) and black tern (Chlidonias niger) and many passerines.