According to Geology professor Atle Nesje of Bergen University, fjords occur where there was glacial activity below where the sea level is as of modern times. Fjords.com notes that Norway and Canada are home to fjords and fjord lakes.
Professor Nesje explains that glaciers may carve a valley and subsequently retreat, which causes the sea to spill into and fill up the bottom of the valley, resulting in narrow inlets linked to the ocean. The origin of the word "fjord" is the Norse "fjörðr," indicating a place one travels across. According to Fjords.com, the word is also linked to the English word "ferry."