The spotted shag is a medium-sized, grey-blue marine shag with a long, slender bill and yellow-orange feet. Adult breeding birds have small black spots on their back and wings.
A distinctive curved broad white stripe runs from above the eye down both sides of the neck. They have a black crest on the front and back of the head.
Bare facial skin between the eye and bill turns green-blue before the breeding season. They make loud grunts at resting, roosting and nesting areas, but are otherwise silent.