While mayflies hatch year-round on the Chattahoochee the month of May is when anglers can expect to see the first great emergence of larger mayflies like Light Cahills, Quill Gordons and Hendricksons to name a few. These three species occur in better numbers on the lower river downstream of Morgan Falls Dam but do also exist in sparse population densities extending upstream on the 35miles north to Buford Dam.
From Morgan Fall Dam down to Paces Mill anglers should be prepared to imitate adults with dry flies as the hatch cranks up with trout often keying in on one size and one color. On the upper reach it is best to imitate the nymph stage with larger pheasant tail nymphs in #12 down to #16 hook sizes.
The Chattahoochee River tail-water has approximately twelve species of mayflies which include all four behavior types or styles of this species in the larval stage which include burrowers, crawlers, clingers and swimmers. These behavior types will help anglers narrow down their selection process while choosing the right nymph and fly fishing tactic. Matching the Hatch by Ernest G. Schwiebert, Jr. is an excellent guide to mayfly hatches and tactics in North America.
As a good general rule of thumb if you see mayflies on the surface but no fish rising it is best to try to match as close to the size of those adults with a nymph imitation with an initial “dead-drift” then a final swing or “Leisenring Lift” as your fly quarters downstream . When fish begin rising you will likely see these larger more visible mayflies actually get eaten by the fish which will allow you to make an obvious choice to switch to dry flies.
Tight lines, Chris Scalley