Saw this critter last week in the shallows at night, via flashlight. Water was quite cold too so I was surprised to see it swimming around in the shalllows.
It has a very ineffective 'kick stroke' and can't seem to move much at all. Must be it tastes bad or it would have disappeared long ago!
Online pictures make me think this is tabanus atratus, the larvae stage of a rather large nasty looking BLACK HORSE FLY Oh RATS! that is right, photobucket is now blurring pictures to encourage us to pay them more.
I'll upload to the forum directly in this message and then delete the one above.
Thanks for letting me know the picture in my first post was bad!