Mayfly

Keys used for
this identification

First gill shorter than gill 7 and not as wide.

Pronotum

Tarsus with a dark band only distal.

Hind margin of tergites with point spines only.

Upper margin of hind femora with distinct row(s) of pointed bristels ventrally, behind the fringe of hairs.

Species
Ecdyonurus venosus

There were many of these Larvae in the strongest currents of the riffles. They were in several sizes.