This photo almost got trashed, but then I noticed the blue dash:
Do you see it, towards the upper right? The swallows were zipping everywhere over the water, but I couldn't even aim the camera at them; they were gone already. Laurie caught this one by accident.
How fast do swallows fly, I wondered. So have other people; and helpful obsessives* have taken it upon themselves to answer the question.
Jonathan Corum calculated the speed of a European swallow at 11 meters per second, or 24 miles an hour. (Go look over his calculations; they're beautiful, as well.) A commenter revised that down to 20 miles an hour; still plenty fast, if it's swooping by your head. And Wikipedia gives an overall average (all swallows) of 30 - 40 km/h for catching insects, and 50 -60 for travelling. (From 19 to 37 miles per hour.)
For comparison, a hummingbird travels at about 25 -30 mph, and dives at up to 60. An eagle flies between 20 - 60 mph, and dives at up to 100 mph. So the swallow is actually fairly slow, but their swooping, winding, back-and-forth style makes them hard to track, even by eye.
*I can relate.