Around 20,000 people race into the lagoon of Puerto de la Aldea, Spain, to gather as many fish as they can with their hands and old baskets. Photos: Desiree Martin/VCG

Tens of thousands of people formed a human chain around Spain's crisis-hit Mar Menor lagoon on Saturday in a show of mourning after tons of dead fish washed ashore, organizers and officials said. 

One of Europe's largest saltwater lagoons, the Mar Menor has long been a draw for tourists but is slowly dying as a result of agricultural pollution, with millions of fish and crustaceans dying over the past fortnight. 

Images of dead fish have traumatized this southeastern coastal region, with locals and tourists turning out to join the mass mourning.

Footage from the scene showed huge lines of people, many in beachwear, holding hands along the waterfront on Alcazares beach, which stretches 6 kilometers and other part of the lagoon's 73-kilometer shoreline. 

"It was an act of mourning for the death of the animals... we wanted people to somehow ask their forgiveness for the barbarity we've inflicted on them," Jesus Cutillas, one of the organizers told AFP.

"For days, we've witnessed the death of millions and millions of fish and seeing all that unnecessary death hurts."

"The aim was to express our regret for what has happened and show our determination that it never happens again."

Many people wore black, others held up banners reading: SOS Mar Menor. Organizers estimated up to 70,000 people joined the protest.  

Experts say the fish suffocated due to a lack of oxygen caused by hundreds of tons of nitrates from fertilizers leaking into the waters, causing a phenomenon known as eutrophication which collapses aquatic ecosystems. 

On Monday, regional officials said they had removed 4.5-5.0 tons of fish, but by Saturday that had risen threefold to 15 tons of fish and algae.

AFP