LA CROSSE -- The National Weather Service says the mayfly hatch on Thursday evening was so large it was captured on radar.

The Minnesota Department of Natural Resources says the short-lived adults found near water have a long tail and large transparent wings.  The larvae are aquatic.

Mayflies can be found in almost all freshwater systems with adequate oxygen levels.  Mayfly larvae feed on algae, fungi, and decaying plant materials.

They are extremely important in the aquatic food web.  As nymphs, they are food for reptiles, fish, birds and mammals.

The adults are often eaten by birds and bats while they are alive.  Once the mass of swarming, mating adults dies there is a literal smorgasbord on the surface of many lakes and rivers when they often number in the millions.

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It wasn't that long ago that many of our rivers and streams in Minnesota no longer had mayfly hatches.  The primary cause of the collapse of the mayfly populations during the 1960s, 1970s, and early 1980s was sewage. Little or no treatment of sewage was happening during that time.  We were literally flushing our toilets into the river in many parts of the state.  Today, because of modern sewage treatment facilities and regulations on the disposal of chemicals mayflies have returned to most waterways.

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