The Mar Menor crisis deepens as oxygen drops and nutrients rise
The worst forecasts have become reality. Since late March, experts have warned that the Mar Menor is trending toward a new green soup caused by heavy rains that carried nitrogen and phosphates into the lagoon. The elevated nutrient load, combined with pollutants from weather events, has raised fears of another anoxic episode and mass fish deaths, an issue that appears to have begun this week.
Earlier today, dozens of dead fish surfaced in the Atalayón area near Santiago de la Ribera, San Javier, and were promptly removed by environmental authorities. In early May, measurements in the Mar Menor showed low oxygen levels in several zones, prompting the monitoring committee to discuss solutions such as oxygenating water with microbubbles in about 150,000 cubic meters of water and across six hectares of surface area.
Sources from the Murcian Institute of Agriculture and Environmental Research and Development and the Mar Menor Observatory indicate persistent low oxygen values in the northern basin. The readings ranged from 2 to 4 milligrams per liter, a concerning level for the season, signaling potential hypoxia in parts of the lagoon. Small and medium fish, primarily gobies, were removed, along with small crabs and shrimps that were collected from the shallower rocky zones.
Technicians from the autonomous research organization monitored 48 sites in the north where these anoxic conditions were detected. Council member Antonio Luengo stated during a morning appearance at the Regional Assembly that the northern basin has shown lowered oxygen levels in recent days, signaling a period of hypoxia in that area.
Civil Guard officers were dispatched to assess the situation and oversee the Castillico beach. ANSE technicians also inspected the removal of samples on the ground. Biologist Jorge Sánchez noted that the current state of the lagoon makes this outcome predictable after several difficult days.
The Ministry of the Environment reports approximately 250 dead fish weighing around three kilograms in total. It notes that this episode aligns with forecasted conditions due to nutrient inputs from the Rambla del Albujón. In response, the action protocol was activated and environmental teams were deployed to monitor and remove affected samples. IMIDA began analyzing other points in the lagoon to determine if additional zones are experiencing low oxygen levels.
UMU ecology professor Angel Perez Ruzafa commented that the recorded oxygen values are very low for this time of year and that eutrophication continues. He pointed out that the nutrient inflows from heavy rains are accelerating the process, and warned that the situation could worsen as summer approaches. He also noted that recent temperatures may contribute to the problem.
The Spanish Institute of Oceanography warned last April that another anoxic episode could occur after torrential rains, which carried runoff and nutrients into the ecosystem and spurred rapid growth of microbiological and phytoplankton communities.
With filamentous algae expanding across much of the lagoon, oxygen deficits have emerged in the past weeks. The Mar Menor faces a real risk of another anoxic event and widespread mortality among marine life, potentially impacting the entire ecosystem in coming weeks.
Negative effects on tourism
Coastal tourism businesses report reservation cancellations ahead of the summer season due to disruptions at the beaches. Local tourism operators fear the Mar Menor crisis will drive visitors away, leaving hotels, restaurants, and other services with far fewer customers if the beaches do not regain their usual appeal in the coming months.