Sulphur hatches are common on the South Holston tailwater from late April thru October and on the Clinch tailwater in May and June. Two species of mayfly are typically lumped together as sulphurs, Ephemerella Dorothea and Ephemerella Invaria.
Ephemerella Dorothea typically hatch when the water is between 60 and 65 degrees and are around a size 16 to 18. Nymphs are commonly found in slower currents and pools, and can ocassionally be found in shallow riffles and are best imitated using pheasant tail and split case nymphs. They emerge in slow pools and tend to congregate in eddies. Emergence takes place just below the surface film and can be imitated using various CDC wing emerging patterns. After emerging from the nymphal shuck the dries drift for an extended period waiting for their large wings to dry. Dries are best imitated with deer hair or CDC wing comparaduns. Adding a bright red head to your fly can help to imitate the big red eyes found on this species. Sometimes the trout can become selective and feed only on the females that have a little green egg-sac on the rear. To date I have only fished one spinner fall, and was not very successful in matching the pattern. The photos at right are of specimens caught on the Clinch River.
Ephemerella Invaria typically hatch when the water is between 52 and 60 degrees and are usually found in slight faster flowing water than their Dorothea cousins. Invaria is also slightly larger than Dorothea at a size 14 to 16 and lack the bright red eyes. Fly patterns for both are similar with exception to the red head on the duns. The spinner is a darker color than the dun and patterns should be chosen accordingly.
Color variation is another issue. The specimens I have found on the South Holston and Clinch vary slightly in the depth of yellow color. South Holston duns appear to be more of a creamy yellow color and Clinch river duns are more of a mix between orange and yellow.
Information for this piece has been compiled from the following websites:
Next up: Common Sulphur Patterns
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