TOPSHOT - A swarm of mayflies (Ephoron virgo - Ephemeroptera of the Polymitarcyidae family) flies over the surface of the river Danube after sunset in Szentendre, north of Budapest, Hungary, on August 9, 2022. - Mayflies insects disappeared from the big rivers of central Europe due to water pollution in the last 40 years, but they started to return around 2012 as a result of a better quality of the water. Reducing and adapting the artificial street lights on the river bank helped also not to attract the night-swarming mayflies away from the water. (Photo by FERENC ISZA / AFP)