This field guide written by J. Guarino, C. Gastador, and E. Miller has useful photos, descriptions, and illustrations of key traits for identifying crayfish species in the White River Watershed, including Orconectes propinquus.
Craysfish are hard to identify when you have the actual animal, let alone from photos. O. propinquus is supposedly one of the easier to ID species, if you can actually see the key traits. The most distinctive feature of these crayfish is a ridge (called a "carina") running down the middle of the three-pronged plate that extends across the top of the head and out between the eyes. Other species lack the ridge on this plate. Unfortunately, the "carina" is often small and difficult to see, particularly in photos. These crayfish are aslo supposed to have orange-tipped claws and a dark band running down the back to the tail, but similar traits are seen in other species, too.