Spain’s unique Mar Menor, 10 years after infamous pollution episode: From the ‘green soup’ to ‘a tiny Mediterranean’

Given the clear waters and the dazzling calm stretching this spring morning from Villananitos beach to the wall of residential buildings on La Manga, a sandspit on the far side of the lagoon, it is hard to recall how the Mar Menor collapsed exactly 10 years ago. A biological breakdown known as the “green soup” devastated the iconic wetland, located in the region of Murcia in southeastern Spain. To this day, although remarkably recovered, the natural space remains in an unstable balance, according to scientists who monitor its vital signs daily.

On the morning of May 27, 2016, ANSE (Association of Naturalists of the Southeast) and the World Wildlife Fund (WWF) issued a press release with a video that set off all kinds of alarms: floating in what looked like a kind of greenish vomit, a diver moved slowly like an astronaut exploring a distant atmosphere. “It was like dropping a bomb; we didn’t expect it would have that kind of an impact,” recalls Pedro García Moreno, a veteran conservationist and director of ANSE.

This episode, dubbed the “green soup,” made global news as it illustrated the pollution of a wetland that had for decades been damaged by mining waste, sewage discharges and untrammeled development, and was finished off by nitrates from the powerful agricultural industry in the region.

Pesticides, brine from desalinating water from wells (themselves illegal in most cases), and most particularly nitrogen fertilizers leached into the wetland from the early 1980s, both on the surface, carried by rain, and through the Quaternary aquifer, a large underground water pocket estimated by the regional government to have stored up to 300,000 tons of nitrates.

The Mar Menor quietly absorbed all this enormous pollution while it could until, shortly before the summer of 2016, a eutrophication crisis erupted due to the excess nutrients, and in subsequent years this triggered episodes of anoxia [absence of oxygen] that killed off millions of fish and crustaceans and wiped out 85% of the seagrass meadows. A natural setting tied to the most cherished summer memories of several generations of Spaniards was dead.

No sign of the seahorse

So what has happened beneath the 66 square miles of water sheet over these 10 years? “The process we know as mediterranization has accelerated: due to the progressive drop in salt levels we have gone from a Mar Menor with its own characteristics, with exclusive species adapted to a singular environment, to a tiny Mediterranean,” explains Miguel Vivas, a researcher at the Spanish Institute of Oceanography (IEO). He says the consequences of this equalization between the two water masses have been “dramatic” for species such as the noble pen shell, a critically endangered giant mollusk that once was counted by the millions in the lagoon. Now only a few thousand remain. The seahorse has likewise been swept away—where millions once lived, it is now hard to see a single one. “And the tita [a marine worm] has simply disappeared after being extremely abundant,” Vivas adds.

Taking advantage of this situation, numerous invasive species have taken up residence in the Mar Menor, such as the huge Atlantic blue crab, which preys on prawns, tears fishermen’s nets and has displaced the native green crab. Other newcomers include the barnacle and the pearl oyster. Strangest of all are the organisms from distant oceans that have shown up in Europe’s biggest saltwater lagoon, such as the mesmerizing Australian spotted jellyfish.

Among the commercial species, gilt-head sea bream and European seabass maintain their abundance with seasonal fluctuations, while eel and the local prawn are “in very poor condition,” says this marine fauna monitoring expert. “Worse, the exotic brown prawn, bigger than the local prawn and worth less at market, is now beginning to be caught. It’s hard to tell them apart and it is sometimes sold mixed in with Mar Menor prawns.”

On land, the “green soup” also shook the local economy. Three studies involving Genoveva Aparicio Serrano, a professor at the University of Alicante and recently published in Ecological Economics and the Journal of Environmental Management, estimate losses of €5,190 ($6,000) per household for residents of the coastal municipalities following the 2016 eutrophication episode. “The environmental shock caused an 18.1% decline in household income compared with areas of the region of Murcia that are not part of the Mar Menor coast,” the researcher says.

Meanwhile, a study by Bank of Spain researcher Gabriel Pérez Quirós estimated a €4.8 billion ($5.6 billion) depreciation in Mar Menor housing units in the years following the green soup outbreak.

A €675 million restoration plan

But this eutrophic decade has also brought hopeful news, with solutions to restore the Mar Menor that began many miles from its shores, including an initiative by the Ministry for the Ecological Transition that has mobilized more than €400 million ($465 million) over four years from a total budget of €675 million ($786 million) for territory restoration projects.

“The large fish die-offs were the trigger for the ministry to take the initiative,” recalls the biologist Francisca Baraza, 72, who was in charge of Water Cycle and Ecosystem Restoration at the ministry. After she had retired, the environment minister at the time, Teresa Ribera, brought her back to lead a complex challenge: to fix up the wetlands of the Mar Menor, Doñana, the Albufera and the Tablas de Daimiel —four natural spaces affected by deficient and in many cases fraudulent water-management practices.

For the Mar Menor, the Framework of Priority Actions has meant creating a green belt around the lagoon, decontaminating the Sierra Minera mountain mining areas, reforestation, river-course corrections, creation of floodplains and more. With 10 lines of action already underway, Baraza looks back in disbelief at “everything that has been achieved in such a short time, considering we started with a blank sheet.”

Meanwhile, the Segura River Basin Authority (CHS) has dismantled 9,100 hectares of illegal irrigation out of more than 50,000 hectares of cropland in the area, 3,500 of which have already been forced to return to their original dryland farm state.

The wetland’s recovery has gained momentum thanks to better coordination with the regional government and local authorities after early years of intense tension. For Francisca Baraza, the “good will” of the regional environment chief, Juan María Vázquez Rojas, has been crucial to advance measures that require agreement. “The Mar Menor is more monitored, more studied and more protected than ever,” Vázquez Rojas tells EL PAÍS. “We have deployed a permanent scientific and technical monitoring network, with continuous control of physical, chemical and biological parameters and predictive systems. Science has ceased to be occasional and has become the axis of daily management.”

The Murcia environment chief also highlights the renaturalization of coastal areas such as the large Carmolí crypto-wetland, the construction of 14 storm tanks to retain runoff during torrential rains, and forest interventions in the headwaters of the basin in the Carrascoy, Altaona and Escalona mountain ranges. Juan María Vázquez also speaks enthusiastically about the future Mar Menor Observatory, a research and species conservation center to be built on the grounds of the former San Javier civil airport.

The elephant in the room remains the Quaternary aquifer, with an extremely high nitrate load that keeps pouring into the Mar Menor. “This summer is going to be very hard,” warns Ángel Pérez Ruzafa, a professor of ecology at the University of Murcia. “Nitrate input has quadrupled compared with last year, phosphorus is rising due to intrusion from blind wells, and salinity has also fallen. It had been recovering for three years but has taken a severe dip.” Pérez Ruzafa, chair of the Scientific Committee that advises the regional government, says abundant winter rains have recharged the groundwater pocket, so that the nitrates have begun to leach into the lagoon in greater volume. At present, about two tons per day enter just via the Rambla del Albujón, a channel that discharges 200 liters of freshwater per second into the wetland.

For this reason, biological production has surged in the form of macroalgae, better known as ovas, which regional workers cannot remove from the shores fast enough to prevent rot and spikes in oxygen consumption. In the first three months of the year, 4,600 tons of biomass have already been removed — more than 45% of all that was collected in 2025.

Under these conditions, “the chances that a new anoxia will occur this summer have tripled. A day when the temperature rises and the wind doesn’t blow, or there is no oxygenation, or the water column is stratified, or phosphorus increases…,” warns Ángel Pérez Ruzafa, who favors extracting contaminated water from the aquifer to denitrify it and make it available to farmers once it has been treated.

As every late spring since 2016, the Mar Menor holds its breath to see what the summer will bring — once its season of splendor, now a season of threat.

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