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.
Time of year : Late June through late July; again from August through October
In 10 records from GBIF, adults of this species have been collected during July (40%), May (30%), June (20%), and September (10%).
In 4 records from GBIF, this species has been collected at elevations of 3, 26, 886, and 1089 ft.
The little nymph can easily crawl out of the water during emergence, and therefore the trout are able to consume them en masse very close to the bank.
Substrate: Gravel, vegetation
There's a great blog post on Aquatic Insects of Central Virginia about identifying Iswaeon anoka.