The Merja Zerga lagoon is a permanent biological reserve by ministerial decree no. 223-78 of 26 Rebia I 1398 (6 March 1978) the most important on the Moroccan Atlantic coast. It is elliptical in shape (9 km long, 5 km wide, average depth of 1.5 m in the channels and 0.5 m in the lagoon). It is a site designated by Morocco when it joined the Ramsar Convention (1980). The typical Merja with hadras and saregs consists of a vast slikke and crowned by a classic schorre of halophilic vegetation. Communication with the Atlantic Ocean via a narrow and sinuous pass, permanent since 1953 although it was obstructed for some time as a result of storms. Hydrological regime subject to tidal balancing. Two permanent freshwater inlets (today with very low flows) flow into the lagoon: the Wadi Drader to the NE and the Nador Canal to the south (which drains the coastal merjas located to the south of the lagoon). Contributions of a groundwater table. All of these conditions induce very large physicochemical variations in water and high biological productivity.

Among the characteristics of the Reserve:

• Flora and vegetation:
  • Phragmites, Scirpus lacustris and Iris pseudacorus on the banks of the Wadi Drader and the Nador Canal. Halophilic vegetation of schorres consisting mainly of Salicornia arabica, S. perennis, S. perennis, Juncus acutus, J. subulatus, Scirpus maritimus and Cladium mariscus.Submerged vegetation: Zostera noltii, S. perennis, S. perennis, S. perennis, Juncus acutus, J. subulatus, and Cladium mariscus.Submerged vegetation: Zostera noltii, Ruppia cirrhosa, Ruppia cirrhosa, Ulva sp. and Enteromorpha sp.
  • Several Eucalyptus reforestation (farms); a poplar grove in the north of Merja.
• Wildlife and animal populations:
  • Abundant but not very diverse benthic microfauna.Limited benthic macrofauna, on rocky substrate, in the gully and the main channel (Ostrea, Crassostrea, Pholas,..). That of loose substrate, dominated by Cerastoderma edule, Venerupis semidecussatus (both exploited) and Solen marginatus in marine sands, and by Scrobicularia plana and Hydrobia ulvae in thixotropic vases.The majority of fish of marine origin are only found at the level of the neck (Sparidae, Soleidae, Mullus and Torpedo ocellae ata are the most common). Amphihaline fish in the channels: Mugilidae, Dicentrarchus labrax, D. punctata but especially Anguilla anguilla which is exploited. Merja Zerga holds the first Moroccan rank for the transit and wintering of Anatidae and Palearctic Shorebirds. In winter, it hosts an average of 15 to 30,000 Anatidae (11 species, the majority of which are Tundra ducks), as many Coots, between 50 and 100,000 shorebirds (19 regular species where Variable Sandpiper and Black-tailed Barge especially dominate, but also Silver Plover, Great Screech, Avocet,... and the extremely rare Slender-billed Curlew) and 1000 to 2000 Pink Flamingos. Among the remarkable species or endangered species that reproduce on the site, include the Crested Lapwing (the only Moroccan locality and known southern limit for the species), the Cape Owl (20 to 30 pairs, emblem of the reserve), the Echasse, the Avocet, the Collared Glareola and the Dwarf Tern. A hundred species of birds frequent the site, making it one of the major sites for Moroccan avifauna.
  • Amphibians, Reptiles and Mammals: usual fauna of coastal areas in northern Morocco (Rana ridibunda, Pleurodeles waltl, Pelobates varaldii, Natrix maura, Mus musculus, Mus musculus, Mus musculus, Gerbillus campestris, Gerbillus campestris, Lepus capensis,... last observation of an otter dating from 1983). In total, 16 species of Amphibians and Reptiles within the perimeter of the reserve, including 4 endemic Moroccans (Pelobates varaldii, Acanthodactylus lineomaculatus, Calcides mionecton, Ch. pseudostriatus) and the rare endangered European pond turtle on the Moroccan coast
• Ecosystems and environments: Undoubtedly the most important coastal wetland in Morocco, with high biodiversity and remarkable avifaunistic population of international value