These two aquatic birds commonly inhabit the same areas and are easily confused, but fear not! I've come up with the perfect solution!
Left: female juvenile Anhinga anhinga "Anhinga", Right: Juvenile Phalacrocorax auritus "Double-Crested Cormorant"
I spotted these two juveniles at the same brackish lagoon where we're camping. This juvenile Anhinga has favored this same branch for the past couple days, and the cormorant was resting on a post watching surrounding adult Cormorants dive for fish.
A great way to distinguish the two is to focus on the shape of the beak. I like to remember by thinking:
Anhinga = A = Sharp, pointed beak, shaped like the letter A
Cormorant = C = Rounded beak, shaped like the letter C
Both birds are impressive hunters, diving for their small fish as their prey. Eventually both species must perch themselves on a low limb or stump to dry out their wings in the sun in order to regulate body temperature and regain flight capabilities, as the water in their feathers can weigh them down.