They are both. Some like the Great Lakes are large, but other places have small lakes.
The group of large lakes in the northern section of the US is called the Great Lakes. They are comprised of Lakes Superior, Michigan, Huron, Erie, and Ontario.
The Great Lakes.
Great lakes
The Great Lakes
"Great lakes " is obviously 2 words, and refers to the group of large lakes in the northeast USA and Southeast Canada.
The Great Lakes
Great lakes
There are a number of large lakes in the USA. Lake Okeechobee in Florida, Lake Tahoe between California and Nevada, and the Great Salt Lake are three that come immediately to mind.
They are collectively known as the 'Great lakes.'
The Great Lakes
North America / Canada - the Great Lakes.