Cormorants are commonly confused with the anhinga because they too dive underwater for their prey. However, there are noticable differences between the two species. Cormorants have hooked beaks and their bodies remain above the surface when swimming, while the anhinga has a pointed beak and its back remains submerged when swimming.

During breeding season, cormorants get small tufts of feathers on their heads, hence the term "double-crested."