This is a tricky one to ID. The forewings
seem to be on the low end of the "crossvein
count" key characteristic. There are paired marginal intercalaries
in the middle area of the fore wing
(kind of visible in photos, verified 100 % under microscope), and the wing and its veins are pale. Keys would seem to point to Callibaetis pictus
in this case, but several other characteristics including size don't fit (pictus
is smaller), and this is a bit out of its range.