The breeze wafting across Playa de los Alemanes, which – tellingly – translates as Beach of the Germans, carries a pungent smell. It’s a lovely, warm summer evening but the beach, just like all others along Spain’s Mar Menor lagoon, is completely deserted. The odd runner makes their way past empty restaurants facing out on Europe’s largest saltwater lagoon in south-eastern Spain. Dogs are the only ones daring to dip a paw into the water, a dark broth of algae with countless dead jellyfish floating on the surface. Marta Añíbarro, who grew up in the area, says the water in the lagoon used to be …