It has cicada-like wings, a caterpillar-like body, mandibles and a large stinger. Also when we threw it into the water, it floated on the surface and swam back to shore very quickly. It also left shells.
Found this by the river.
Don't know what your bug is but that 'stinger' looks like an ovipositor for laying eggs.
Image too blurry for a positive i.d., but appears to be an insect whose immature stages are aquatic.
Pic to small and blurry to tell but probably one of the fish fly species or a dobson fly. Leaving shells behind is confusing to me but the dobson fly deposits a white egg sac that has a shell like appearance. Other than being a fisherman, I have no other experience with aquatic insects.