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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington
Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Great Lead-Winged Coachmen

This common name refers to only one genus. Click its scientific name to learn more.

Mayfly Genus Isonychia

These are very rarely called Great Lead-Winged Coachmen.
Sporadic hatches are rarely as outstanding as those of Isonychia. On streams with good populations, they are reliably hatching in light numbers, here and there, for most of the evening through most of the mid- to late season.

The spinners, and occasionally the duns, produce more concentrated action, but the real value of the Isonychia hatch is its duration and the size of the flies; large trout become ever watchful for them, even when they aren't emerging.

All the species of Isonychia are similar in appearance and behavior.
Lateral view of a Female Isonychia bicolor (Isonychiidae) (Mahogany Dun) Mayfly Dun from the Namekagon River in Wisconsin
Lateral view of a Female Isonychia bicolor (Isonychiidae) (Mahogany Dun) Mayfly Spinner from the West Branch of Owego Creek in New York
I collected this female together with a male.
Dorsal view of a Isonychia bicolor (Isonychiidae) (Mahogany Dun) Mayfly Nymph from the Beaverkill River in New York

References

Great Lead-Winged Coachmen

Scientific Name
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