In areas where both the Great White Pelican and the Dalmatian Pelican occur (such as Greece), they are sometimes difficult to distinguish.
However, the Dalmatian Pelican has a light iris, whereas the Great White Pelican has a dark iris.
Furthermore, the throat pouch of the Dalmatian Pelican is orange-red; in the Great White Pelican, it is yellow.

Lake Kerkini, Greece, 29 July 2017