I found this insect in the water where the Snake River intersects the St Croix River. From its appearance and the habitat in which I found it I believe that is a type of dark fishfly, probably Nigronia serricornis. Dark fishfly are members of the Corydalidae family, which includes fishflies and dobsonflies, that are usually found in clean stream and rivers with rapids. The Nigronia serricornis dark fishfly has less white on the wings then other dark fishflies which is why I believe that it is this type. The only mystery is the length of the antennae, which is much shorter in the picture then they usually are. It is possible that it might have lost part of its antennae, maybe to a predator.