meaning in context - 'Great Lakes' is or are? Which one is correct?

In this article, I read the following lines:

The Great Lakes have claimed thousands of ships since European explorers began navigating the waters in the 1600s, but few have captured the public's imagination as has the Edmund Fitzgerald, which sank on Nov. 10, 1975, in Lake Superior.

To my mind, 'The Great Lakes' has claimed is correct.

Then I searched for 'the Great Lakes' and I got the following meaning from here:

The Great Lakes (also called the Laurentian Great Lakes,1 or the Great Lakes of North America) are a series of interconnected freshwater lakes located in northeastern North America, on the Canada–United States border, which connect to the Atlantic Ocean through the Saint Lawrence River.

My questions are: The Great Lakes looks a collective noun for a series of lakes, then why 'are' is used every time with it? Shouldn't they put 'is' instead of 'are'?

Answer

Both are possible. The difference isn't even in the meaning but of your preference. The expression

The Great Lakes are a series of...

points to the treatment of the lakes as several elements of one sequence ("series"). The expression

The Great Lakes is a series of...

points to the fact the those several elements constitute one single collection of elements.

Now, depending on the context (and it's provided by the remainder of the sentence), you can deduce whether singular or plural is necessary, or, if you decided to use one or the other, you need to keep it consistent. You can notice that the last clause in that entire sentence has the verb "connect". The use of that form prompts us to think that the plural is intended. Hence the verb "be" (before "a series") has the same form.

The Great Lakes (also called the Laurentian Great Lakes,1 or the Great Lakes of North America) are a series of interconnected freshwater lakes located in northeastern North America, on the Canada–United States border, which connect to the Atlantic Ocean through the Saint Lawrence River.

The relative pronoun "which" in the last [subordinate] clause relates to "the Great Lakes". If you use "is", then the word "which" will relate to "a series", which is singular, and hence you'd write

... , which connects to the Atlantic Ocean through the Saint Lawrence River.