The Newfoundland comes from Newfoundland's island. It's the descendant of the indigenous dogs and the big black bear dogs, brought by Vikings after the year 1001. The size of a dog might be a result of big mastiff dogs, which have been brought by Portuguese fishermen.
In 1610, when the island's colonization started, the breed already had its own physical characteristics and its natural behavior. That's how it could resist to the rough conditions. It was used to pull fishnets and heavy equipment and also to rescue people from the water.