A low head dam on the Great Miami River in Hamilton, Butler County, Ohio. This dam is across the street from the Miami University-Hamilton campus. Low head dams are dangerous, as the sign notes, and this one has claimed a few lives over the years. There's a second low head dam upstream from here, and together the two dams serve to create a pool of water for the once flourishing Hamilton paper industry and other factories. I doubt they'll ever remove these dams, since the pool is useful for the water skiing contests that Hamilton hosts in the summer. It sounds laughable, but it's a big deal. I've seen recordings of some of the contests on ESPN, and they are even duller than televised poker contests. During the summer, there seems to be very little insect life between the two dams. But immediately below this dam, you can find some good stuff, including state endangered Plains Clubtails, like this one:

May 27, 2010.
Plains Clubtail (Gomphus externus).
Great Miami River, Hamilton, Butler County Ohio.

Video recorded on December 18, 2010.