The biodiversity of Ephemeroptera in the Kiamichi River watershed is descri
bed. Fifty-six species, 29 genera, and 11 families of Ephemeroptera are doc
umented in the Kiamichi River watershed. The family Baetidae accounts for a
lmost one-third of the total number of species collected. Fourteen species
are reported for the first time from the Interior Highlands, and thirty spe
cies represent new state records for Oklahoma. Seventy-five percent of the
mayfly species collected from this watershed have strong affinities with ea
stern North America.