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.
Taxon on Aug 12, 2007August 12th, 2007, 8:06 am EDT
Male spinner. Isonychia ?
Yes, it would appear to be. There are (at least) three Isonychia species recorded from Maine, I. bicolor, I. georgiae, and I. obscura. Although the greatest statistical likelihood would be I. bicolor, reliable identification to species requires microscopic examination of male imago genitalia.
Luckily, we have a mayfly entomologist actively participating on this forum, who is qualified to make such an identification, if sent a preserved specimen. See this thread.