Lambrey have a circular mouth on the bottom of their head, something along the lines of what an alage eating fish would have.
They also wouldn't spend much time at the surface as they are somewhat shy.
Approximately what size was it? Where are you located? How deep was the water? Salt? Fresh?
There are some waterborn insects that'll hang from the surface tension of the water and catch fish, but they prefer weedy hunting grounds. They're also a bit smaller, the largest I know of being about 6" long.
Also, are you 100% sure it's alive not just bobbing with the current, or fish knocking into it? I did some photo shopping of the image and I couldn't get any usefull detail out of it, then again it's a blurry image to begin with.