Spain’s largest inland sea loses recovery capacity

by Lorraine Williamson
illegal wells

MURCIA – The massive fish kill suffered by the Mar Menor on Spain’s Mediterranean coast shows that the inland sea has lost its self-regulating capacity. However, if a solution to the discharge problem is found quickly, it is not too late. 

This was confirmed by the Oceanographic Institute of Spain (IEO-CSIC). It concerns discharges of wastewater from intensive agriculture in the area near Mar Menor. A report prepared at the request of the Ministry for the Ecological Transition and the Demographic Challenge (Miteco) confirms there has been an improvement in the oxygenation of the water in early September. And that furthermore, it may be related to the change in the local wind regime. 

However, in this sense, the apparent improvement may be transient. Because organic matter saturation and turbidity still persist. As does the risk of possible new hypoxia (lack of oxygen) and anoxia (lack of oxygen supply). 

The document confirms that the massive fish kill in Mar Menor last summer is not due to summer temperatures. Although these were lower than the average of previous years. Also, the decline is not due to a ‘gota fría’ with heave rainfall, as in 2019. However, the mortality is clearly attributable to the ingress of fertilisers. Which is a result of mass farming and other human activities on the banks of the lagoon. 


Nutrients and organic matter play a fundamental role in promoting the eutrophication of the lagoon. Eutrophication is the unwanted excess of nutrients that leads to explosive algae growth. Mar Menor has an excess of phytoplankton which has limited the access of light into the water. That affected the availability of oxygen to such an extent that it was almost hypoxia. 

Nevertheless, experts confirm the recovery of Mar Menor is possible if the human cause is addressed. And also essential characteristics such as salinity are taken care of. Conversely, if the same situation persists, undergrowth may die, further exacerbating the environmental crisis. 

Enviro organisation wants Mar Menor nature zone 

Ecologistas en Acción has submitted a proposal to the Ministry for the Ecological Transition and the Demographic Challenge to create a strip of nature around the Mar Menor. It would concern 15,000 hectares, about 12% of the catchment area. This would limit agricultural and urban activity around the inland sea with the aim of contributing to the solution of the eutrophic crisis in which the lagoon is located. 

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The new nature reserve should be free of crops and buildings. So that the natural vegetation and its ecological functions are restored. Such as wetlands in flooded areas and undergrowth typical of such an environment. Because this helps to retain fertilisers and sediments, among other benefits. 

The environmental organisation believes that the measures proposed so far were only aimed at limiting the influx of nitrates. With this, the organisation refers to the approval by the government in Murcia on Monday of a bill to amend the Mar Menor Protection Act to limit the access of nitrates into the lagoon. Ecologistas en Acción believes that action must also be taken against the diffuse pollution in all water supplies that form the main gateway for sediments and phosphates. 

Furthermore, it appears an important part of the supply of nutrients takes place when during floods, pollutants that accumulated in the environment over months or years flow through all drainage channels to the inland sea. This is especially after heavy rainfall.

Natural wetlands, according to Ecologistas and Acción, are the only systems capable of reducing the nutrients carried during floods. No civil work surpasses this. 

Satellite images show state of Mar Menor 

The current state of the Mar Menor can be observed from space. This is thanks to the image taken on September 12 by the two Sentinel 2 satellites of the European Union’s Copernicus observation program. The images clearly show the turbidity of some strips of the Mar Menor. 

As part of the Sen2Coast project of the Higher Council for Scientific Research (CSIC), satellite images have been published showing the turbidity of some strips of the Mar Menor. 


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