Some 20 tonnes of dead fish have washed up on the shores of one of Europe's largest saltwater lagoons in Spain, sparking protests against deteriorating environmental conditions while local prosecutors opened an investigation.
Once a magnet for tourism and a sanctuary for marine life, the Mar Menor in Murcia, on Spain's southeastern Mediterranean coast, has seen fish stocks plummet in recent years, with similar mass die-offs occurring in 2016 and 2019.
Residents began seeing dead fish and crustaceans on Monday.
"They are still washing up today. We calculate that some 20 tonnes have died to date," said Jose Luis Garcia, director of the World Wildlife Fund's marine programmes in Spain.
While the regional government blamed the deaths on recent high temperatures, ecologists have warned for years that runoff from nearby agricultural facilities and pollution from urban development has severely degraded the water quality.
"People call it the green soup" explained Ramon Pagan of the Pact for the Mar Menor pressure group. "It's caused by an excess of fertilisers in the water...particularly from intensive agriculture."
High levels of phosphates and nitrates in the water cause huge blooms of algae to flourish. These block out sunlight from penetrating the water and reduce oxygen levels below the surface, eventually suffocating the marine life.
Scores of protesters wearing 'SOS Mar Menor' t-shirts gathered on the shore and chanted "We want solutions."
"We have been demonstrating about this for years," said Ana Pineda of the Urrutia residents' association. "We've been unable to set foot in the water or be on the beach for years."
Digging into the beach with her foot a few metres from the shoreline she uncovered a layer of thick black sludge beneath a thin covering of sand.