A yellow swallowtail, a new species to me. I've seen many similar looking ones in flight recently, but hadn't caught an image yet. The swallowtail species in the area would all eventually land on the river bank on a sandy shoreline (uncommon, mostly granite or dirt shores on this section of river) next to a flowering meadow. This made it easy to wait and catch them there. I assume this is how they drink, since they usually landed very close to the water's edge and paused for a bit before flying again.