"The fresh water tends to flow on top of the salt water because the salt water is heavier," said Tom Kutcher of Save the Bay.
In areas where you have fresh water inflow, they tend to freeze first.
Take for example the deep freeze of 1994. The West Bay was frozen to the Jamestown Bridge and Coast Guard cutters were necessary to keep commerce going.
"My mother told me a story when she was a kid she grew up in Warren, she remembers that there was a fire on Prudence Island and they took the Warren fire trucks and drove across the ice," Kutcher said.
You need to sustain average temperatures well below average to get significant parts of Narragansett Bay to freeze over.
On Thursday, there's just a thin layer of non-contiguous ice off Goddard Park.
Compare that to January 1982, where temperatures were seven degrees below average.
In January 1981, it was even colder. Temperatures were eight degrees below average. It was so cold, heating oil tankers couldn't get through the ice on the way to Nantucket.
In comparison, we're averaging about one-and-a-half degrees below average for this month.
Also something to keep in mind, the summers that followed those arctic winters, on average, were hotter than usual.