Hendrickson

This hatch marks the start of serious mayfly action on almost every major trout water in the East and Midwest in the early spring.

The emergence begins in early April in the trout streams of southern Pennsylvania. It peaks in mid-May in the Catskills and late May farther north. It can linger through early June in northern areas like the Upper Peninsula of Michigan. Good action lasts from two to three weeks on any given river.