Thanks for the input, I wouldn't necessarily call it slack water, where I was stream sampling, it was in shallower water adjacent to some deeper water with current.
This bug was wide in the middle, like a beetle, sorry I didn't get better pics to display that.
from the pics i would say a clubtail larva (black gragon fly) found mostly in the eastern US. they like clean water running..
Taken from "Aquatic Entomology" (McCafferty, patrick)