The Mar Menor is facing one of its most critical situations in recent years this summer. Alarm bells are ringing among scientists and managers due to the accumulation of risk factors, including rising surface water temperatures, jellyfish blooms, and increased levels of nutrients and nitrates in its waters. According to experts, all of this places the lagoon's ecological balance in a precarious position, making it susceptible to abrupt changes in the face of any extreme weather event.
With water temperatures reaching or exceeding 32 degrees Celsius at the start of summer, the consequences for the flora and fauna of the Mar Menor could be severe. Episodes of hypoxia, a dangerous decrease in oxygen levels in the water, threaten to recur after four years in which, despite environmental pressure, the ecosystem had shown some capacity for self-regulation . However, the combination of heat and nutrients is testing the resilience of this unique enclave on the Murcian coast.
Heat records and risks of hypoxia
Official records have reported record-breaking temperatures in the Mar Menor lagoon , reaching up to 32 degrees Celsius at the surface, a level not seen in the last two decades. This increase directly affects dissolved oxygen levels, exacerbating the danger to aquatic life . Professor Ángel Pérez Ruzafa, a researcher at the University of Murcia, has warned of the high risk of hypoxia episodes and the negative consequences for fish and other aquatic organisms.
The expert points out that " we are on a knife's edge " and that we must not let our guard down in such a volatile situation. The combination of high temperatures and possible periods of calm seas could trigger serious events in a few days, especially if the influx of nutrient-laden water continues.
Massive input of nutrients and torrential rains
The massive influx of nutrients , primarily from the El Albujón ravine and the water table, has increased following the torrential spring rains . Peak flows of up to 22.000 liters per second of water contaminated with nitrates and other agricultural substances have been measured, stagnating in the lagoon. This is exacerbated by the silted-up aquifer and the constant leaching of fertilizers.
The most recent scientific report indicates that the contribution of nutrient-rich water increased significantly compared to the previous year, and that the rains of March 2025 represented a critical point. Although the water's clarity, reduced turbidity, and low chlorophyll levels appear to be maintained, a clear vulnerability to any sudden disturbance is recognized.
Managing the aquifer level is considered a priority by scientists, who are calling for coordinated efforts between regional and national administrations to limit the arrival of nutrient-rich waters and prevent the formation of "green soups" or harmful algal blooms.
Specific installation of anti-jellyfish nets
In anticipation of a new jellyfish bloom similar to last summer's, the Mar Menor Directorate General has decided to install, as a temporary measure and with the support of the Scientific Advisory Committee, jellyfish nets at four specific locations: Villananitos and Lo Pagán (San Pedro del Pinatar), and Veneziola and El Pantalán in La Manga (San Javier). This measure responds to municipal demands and the proliferation of the "fried egg" jellyfish (Cotyloryza tuberculata), along with other species present in the lagoon.
The aim is to ensure the safety and comfort of swimmers during peak season while minimizing the impact on the marine ecosystem. Tasks include weekly cleaning and replacement of the nets, transport and placement using floating systems to reduce impact on the seabed, and continuous biological monitoring. Additionally, the presence of protected species, such as seahorses, will be monitored during the removal of the barriers.
Installation is scheduled to begin in mid-July, allowing enough time for the jellyfish to reach a size that prevents them from passing through the nets, improving the system's efficiency and reducing disruption.
An increasingly fragile ecological balance
Regional officials and scientists agree that, despite the recovery capacity demonstrated in recent years, the ecological state of the Mar Menor remains extremely delicate. Among the factors maintaining its integrity are the systematic removal of biomass from the beaches and constant environmental monitoring , actions carried out over several seasons that have helped keep nutrient levels under control, although they remain highly sensitive to external changes.
One of the main challenges is to effectively reduce nutrient runoff from both surface and groundwater, as well as to foster collaboration among government agencies to implement technological and land-use management solutions. The report highlights the importance of intensifying preventative measures, investing in science, and managing the environment responsibly to avoid further vulnerability.
The combination of extreme temperatures, heavy rainfall, and complex management makes this season a real test for the Mar Menor. Although it has held up so far thanks to scientific and administrative efforts, with each passing summer, the pressure on the resilience of this unique coastal ecosystem increases.