Expect to see them in the millions any day now. They don't bite or sting, but they will cover the entire surface area of any stationary object.
Adult mayflies only live for about a day, and their only purpose besides being a general nuisance is to reproduce. The eggs and larvae can live at the bottom of the lake for around two years until they mature.
There's no foolproof repellent that will get rid of them, but MayflyNews suggests using a broom or leaf blower. Using a hose will just leave an awful, fishy mess.
Photos of the swarm are already starting to surface from out west, so here's a look at what we can expect, thanks to Twitter.
Invasion of the mayflies pic.twitter.com/ER2yW7fTEC— Benjamin (@frankartb) June 24, 2015