TOPSHOT - Dolphins swim in the Tagus past a boat observing marine species off the coast of Lisbon on August 7, 2021. - Since the start of the Covid-19 pandemic, dolphins have returned to the Tagus estuary in Lisbon, where they have found an unusual calm in less polluted water, thanks to restrictions which have led to a drop in maritime traffic, according to scientists. (Photo by PATRICIA DE MELO MOREIRA / AFP)