La Manga and the Mar Menor: a sandbar between two seas

La Manga del Mar Menor is a narrow inhabited sandbar with two different seas at its edges. The Mediterranean meets its eastern beaches, while the shallower, saltier Mar Menor lies to the west. That striking geography is natural, but the continuous road, apartment towers, marina and summer resort were built over it from the 1960s. Understanding the place means holding the sandbar, urbanisation and damaged lagoon in the same view.

The barrier which made a lagoon

The Mar Menor began as an open Mediterranean bay. Waves and coastal currents moved sediment southwards, building a sandy barrier against existing rocky and volcanic outcrops. The resulting strip is about 22 kilometres long, crossed by channels known as golas which exchange water with the open sea. Behind it, the lagoon covers about 135 square kilometres but is no more than seven metres deep.

Official conservation material describes the Mar Menor as the largest hypersaline coastal lagoon in the western Mediterranean. That is more precise than the frequent claim that it is simply Europe's largest salt lagoon. Its soft sand and mud beds, five volcanic islands and salinity support a distinctive ecosystem. The barrier is therefore not just land between beaches. Its shape and openings govern how the lagoon exchanges water.

From dunes to a built-up strip

Before large-scale construction, La Manga held dunes, scrub, salt-working sites and the traditional encañizada fishing channels. Developer Tomás Maestre assembled land for a resort plan by the architect Antonio Bonet Castellana. Four estates received official tourist-interest declarations between 1966 and 1969. Roads, apartment buildings, hotels and the Puerto Deportivo Tomás Maestre then established the long urban form seen today.

The project altered shorelines as well as adding buildings. Lagoons and marina basins required filling, dredging and new channels, while the Gran Vía became the principal route along the strip. Some dune and wetland fragments survive, especially around Las Amoladeras and towards the protected northern end, but they should not be read as untouched scenery around an otherwise harmless resort. Current dune restoration work responds to decades of pressure from urban development.

One place divided between two councils

La Manga has no ayuntamiento or municipal boundary of its own. Its southern section belongs to Cartagena and its northern section belongs to San Javier. The division crosses a settlement which functions as one long corridor, so public transport, policing, emergency planning and seasonal services require coordination between both councils. La Manga Consorcio was created for that shared work.

This also explains why there is no single INE population figure for La Manga. Residents are counted inside their respective municipalities and seasonal occupation changes the practical load on roads and services. On the Explore map, San Javier provides the distinct linked municipal polygon because Cartagena already links to the city guide. The article itself covers both administrative sections and should not be mistaken for a San Javier-only account.

A lagoon pushed beyond balance

The Mar Menor's environmental crisis is driven principally by excess nutrients and organic matter reaching the lagoon from the Campo de Cartagena. Intensive agriculture is the largest source identified by the Spanish Institute of Oceanography, alongside urban, mining, livestock and other pressures. Nitrates and phosphates encourage phytoplankton growth. Dense blooms block light and their decomposition reduces dissolved oxygen, damaging bottom vegetation and animal life.

A major bloom turned the water into the so-called green soup in 2016. An anoxic episode after torrential rain caused mass mortality in 2019. In August 2021 advanced eutrophication and hypoxia brought another mass death of fish and crustaceans. The IEO found no evidence that water temperature was the trigger for the 2021 event. It traced the main cause to continuing nutrient inputs which began a phytoplankton bloom around the Rambla del Albujón.

Rights, monitoring and a visit now

Ley 19/2022 took an unprecedented legal approach by declaring the Mar Menor lagoon and its drainage basin a legal person and a subject of rights. These include the rights to exist, evolve naturally, be protected, conserved and restored. The law also allows any person or organisation to defend the ecosystem before a court or public administration. Legal personality does not itself clean the water, but it changes who can speak for the lagoon and how harm can be challenged.

Recovery remains active rather than complete. MITECO and IEO-CSIC publish scientific monitoring, while the regional Canal Mar Menor provides current oxygen, chlorophyll, salinity, turbidity and transparency data. A bathing-water result answers a narrower public-health question and is not a verdict on ecological recovery. Before swimming or boating, check current official notices and weather, respect dune closures and avoid disturbing shallow vegetation.

South-west, Cartagena's harbour and naval city explain the council responsible for lower La Manga. The archive article La Manga del Mar Menor remains supporting background rather than the source of this commissioned account.

Sources and review

Reviewed in September 2026 using the Región de Murcia's official protected-site record for the lagoon's area, depth, barrier and western Mediterranean status, Región de Murcia Digital's development history for the Maestre and Bonet plan, San Javier's joint emergency record and Cartagena's council proceedings for the split administration, MITECO and IEO-CSIC's 2021 scientific findings for the eutrophication and mortality sequence, the official text of Ley 19/2022 for legal personhood and the regional Canal Mar Menor for continuing monitoring. Environmental conditions, access controls and bathing notices change, so consult the responsible authority before travelling.