Mayflies have aquatic larvae that are sensitive to water pollution. Their absence can indicate poor water quality and high pollution. The Danube River near Tahitotfalu, Hungary was once a site of large mayfly swarms but the water was degraded by high levels of phosphates, nitrates and sewage. These pollutants can lead to conditions that deplete oxygen in the water. The mayflies cannot survive in low oxygen water and the mayflies disappeared from that stretch of the Danube.
Recent efforts have greatly reduced levels of phosphates and nitrates and upgrades to sewage treatment systems have left the water much cleaner. Now mayflies are able to grow and thrive in the river once more. This week, the mayflies put their stamp of approval on the cleanup efforts with the first swarm in 40 years. Millions of the mayflies emerged from the water covering the area with a blizzard of mayflies. Welcome back and here’s to good river health!