The dog fell into the frigid waters near the Eliot Bridge around 3:50 p.m., the department said.
The sandy-colored dog’s head was above water, as firefighter Sean Williams slid toward it on a rescue board, photos posted on Twitter show.
The firefighter and dog were pulled to shore by a rescue crew. One person shouted, “Come on! Good girl,” and other words of encouragement, according to a video posted on the department’s Facebook page.
Safely ashore, Williams and the dog were greeted with applause.