This lagoon, linked by a 900-metre channel to the sea, is part of the El Kala complex of wetland depressions. The Site also comprises a small brackish delta with Salicornia and Juncus species, and a smaller temporary freshwater lake which is fed by precipitation and groundwater and surrounded by a complex of sand dunes. The double exchange of Lake Mellah with its watershed and with the sea through the channel has given a rich biodiversity to the lake. The Site is important for waterbirds that use it as a staging and resting site during their migration, to feed on the abundant supplies of fish, invertebrates and bivalves, or to nest. The 52 species recorded (of which 14 were migrants, 19 nesting and 20 wintering) include the great cormorant Phalacrocorax carbo, the great crested grebe Podiceps cristatus and the tufted duck Aythya fuligula. The salinity gradient and high productivity in the lagoon contribute to high phytoplankton, zooplankton and fish biodiversity, and it acts as a nursery and growing site, especially for eels before they travel to the Sargasso Sea. Thus its most important socio-economic role is the provision of employment for fishermen. Local people also grow peanuts and raise livestock, which has caused over-grazing in some areas. Along with the Ramsar Sites at Lac Oubeïra (Site no.280) and Lac Tonga (Site no.281), El Mellah is part of the El Kala Biosphere Reserve.