Looked like a tiny walking stick, moving very slowly. While members of this family are typically found at ponds, this one was found along a sluggish stream. There was some algae along the bank for it to walk around on.

Nicely enough for purposes of ID, all Nearctic marsh treaders are in the genus Hydrometra.

How to Know the True Bugs indicates some Hydrometra species are wingless as adults, while others are winged. The individual I photographed was wingless, so it is either one of the wingless species, or else a nymph.