A Casco Bay Lines ferry heads to Portland through sea smoke early Friday morning in temperatures well below zero.

A rising sun colors sea smoke rising around lobster boats in Cape Porpoise harbor.

Temperatures in Portland reached as low as 8 below zero Thursday morning.

Sea smoke forms Thursday morning off the shore of Cushing Island.

Joanne Arnold walks the rocks leading to the Spring Point Ledge Lighthouse in South Portland while "sea smoke" rises in the background. The smoke is formed by cold air hitting the warmer layer of air above the ocean. Temperatures reached as low as 8 below Thursday morning.

Joe Carter of Arundel shoots video of sea smoke rising in Cape Porpoise on Thursday, January 8.

The rising sun colors sea smoke rising behind Goat Island Lighthouse and frozen mud flats in Cape Porpoise harbor .

Plumes of steam blow from the Wyman Station power plant on Cousins Island in Yarmouth on Thursday. Temperatures were expected to moderate Friday.

Passengers brave a subzero temperatures to ride on an outdoor deck of a ferry making its way through arctic sea smoke off Portland on Thursday. It may have been cold, but it didn't break any records.

A man shields his eyes from the sun as he views the sea smoke rising from Casco Bay in Portland on Thursday.

A fisherman works aboard a trawler passing House Island in Casco Bay off Portland, where the temperature at dawn was minus 8 degrees Thursday. Sea smoke is a fog formed by extremely cold air moving across warmer water.

Commuters leave the Casco Bay Ferry terminal after arriving in Portland early in the morning Thursday, when subzeros temperatures persisted into the morning.

A woman photographs sea smoke rising from the harbor in Portland, where the temperature at dawn was minus 8 degrees on Thursday.