What waterway leads from the Great Lakes to the Atlantic Ocean?

It is the St. Lawrence River?

Yes.

The waterway that leads from the Great Lakes to the Atlantic Ocean is the St. Lawrence Seaway. To find the answer to this question, you can use a search engine, such as Google, and type in "waterway from Great Lakes to Atlantic Ocean." The search engine will then provide you with the answer, which is the St. Lawrence Seaway.