Four municipalities lie by the Mar Menor, Cartagena, Los Alcázares, San Javier and San Pedro del Pinatar. With a surface area of nearly 170 km², a coastal length of 70 km, and warm and clear water no more than 7 metres in depth, it is the largest lagoon in Spain.
The lagoon is separated from the Mediterranean Sea by La Manga, a sandbar 22 km in length whose width ranges from 100 to 1,200 metres, with Cape Palos in its south-eastern vertex making for the lagoon's roughly triangular shape. There are five islets located within the lagoon, namely Perdiguera islet, Mayor islet, Ciervo islet, Redonda islet and del Sujeto islet.
Its relatively high salinity, which aids flotation, and remarkable sporting infrastructures makes it a popular place for a wide variety of water sports.
Ecological importance of the Mar Menor
At the northern end there are salt-flats which include a wetland of international importance. This area is preserved as a natural park administered by the regional government. Its Spanish name is "Salinas y Arenales de San Pedro del Pinatar". The microbes that live in this coastal lagoon have been recently described. 
The islets and the few coastal places without permanent human constructions are protected by the natural park Islets and open areas of the Mar Menor
In 1994 the Mar Menor was included on the Ramsar Convention list for the conservation and sustainable utilisation of wetlands. The Mar Menor is also part of a Specially Protected Area of Mediterranean Importance and is a Special Protection Area (ZEPA in Spanish) for bird life.
In July 2016 pollution was reportedly so severe as to render the area close to ecological collapse, following 18 years of neglected warnings. The public prosecutor's office is investigating allegations of negligence against the relevant authorities, which are governed by the conservative People's Party 
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