I believe the picture is one of a backswimmer. Very similar to a water boatmen. Backswimmers fly and they can bite. I have had them periodically over the last several years. You have to kill them or direct them into the filter to get rid of them. They are not agressive though. They usually swim away when you get near.

See link for more info
http://ohioline.osu.edu/hyg-fact/2000/2037.html