Dead mayfly goo. From a previous hatch the morning-after on State Highway 43 bridge linking Winona and Wisconsin on a previous hatch. Vulnerable spans at 30-mile intervals are the ways to cross the Mississippi.
A one-day wonder: Hatch, breed, die
WINONA, Minn. — Snowplow drivers are bracing for the cyclical hatch of mayflies in the Mississippi River mud. The mayflies die by the millions after a brief lifespan, only a day. Their carcasses can pile so deep that riverside roads become a traffic hazard. It takes snowplows to clear the way. In the past there have been accidents, some with fatalities, as drivers lose control on mounds of slippery mayfly carcasses. Especially vulnerable are bridges with illuminated traffic lanes that attract mayflies. Until the hatch occurs — nobody is sure exactly when it’ll be —the state Transportation Department is turning off lights on Mississippi River bridges at Red Wing, Wabasha and Winona. An exception is the complex Intestate 90 bridge at Dresbach whose spaghetti ramps and crossovers would be additionally treacherous without lighting. Another exception is the red and green navigation lamps on the underside of bridge decks. These lamps help riverboat captains keep their barge arrays in the navigation channel between abutment piers.