Time has no dimension for aquatic insects. Years underwater for an aerial orgasm of a few seconds for millennia. Of course, the eternal ephemeral exists, but in forty centimeters of fresh water! Manna of summer evenings, the ephemeral is lost in the flights of love. Two years in the water, up to thirty two larval metamorphoses for only a few aerial minutes of pleasures in love. Its world is very unfair but so logically calculated to perpetuate the species. Too many predators in the water for such a sensitive moment, love becomes aerial. It saves eternity from the ephemeral. The mayfly larvae graze on encrusted algae that invade submerged rocks. Phosphates and nitrates spilled in large quantities in river waters favor the development of such algae. Without the mayfly larvae, our rivers would suffocate. They would be eutrophicated. These larvae are unfortunately very sensitive to pollutants such as pesticides, insecticides, heavy metals, hydrocarbons, detergents. They disappear over time and harmful algae invade the river. Mayflies are excellent bioindicators of the health of our fresh waters. They are the oldest winged insects on the planet. The ephemeral disappears, taking away the eternal.