This Water Boatman is one of 125 species in the family.  They are all very similar in appearance, dark brown to black, large eyes, powerful oar-like legs, a little more than 1/4 inch long (5-6mm). They are very difficult to identify, even to genus, by photographs alone. Most require examination of the genitallia to be sure of species identification.  These boatmen swim right side up, whereas the backswimmers swim upside down.