Possibly two questions in here: Are these sentence constructions logical, and if they are, why are they different?
I swam across the Ocmulgee River.
I swam across the Pacific Ocean.
I swam across the Red Sea.
I swam across Lake Winnipeg.
I can't think of a way of phrasing the lake example while using an article with a proper noun. I thought at first it was because Lake Winnipeg is different; it's generic portion (the "Lake") comes first and the name of that body comes second, but I swam across Falls Lake is the same.
Yet the sentence I swam across the lake sounds right to me. …Why?
Best Answer
I'd say you are correct about the placement of the generic word being the reason for using (or not using) 'the' , and all your examples are phrased correctly. Notice that 'Falls' is different also in that it is a plural.
Edit: I have found the answer:
From Wikipedia:
From Monmouth University: