In Northern Michigan, in the heat of the summer, every river essentially becomes two. There is the river of the midday sun - and there is the river of the night. Up here, the river sleeps during the day. And so should you. It's only after the sun sets that the water comes alive.
The occasion is the annual hatch of hexagenia limbata, the giant mayfly, most often simply referred to as the hex. It's a fitting name, a hex is a spell, and like all spells, best cast under the cover of darkness.