The Peaks Island ferry heads out on Tuesday morning across Portland Harbor as sea smoke rises around it. Sea smoke is formed when very cold air moves over warmer water. (Troy R. Bennett | BDN)

A tanker ship (above right) sits at anchor in Portland Harbor on Tuesday as sea smoke rises around it and the Peaks Island ferry heads back to the mainland. The sunrise temperature was 6 below zero. (Troy R. Bennett | BDN)

A tug boat sits moored off Portland’s East End on Tuesday morning at sunrise. (Troy R. Bennett | BDN)

Tuesday morning: A fishing boat (above, clockwise) steams out of Portland Harbor, the sun rises out of the clouds and a common merganser floats on the water. (Troy R. Bennett | BDN)