The King James Version was first translated 400 years ago by the Church of England and the language is somewhat archaic. It also eliminated seven books from the Catholic Bible.
This is the NABRE translation:
1* Then one of the seven angels who were holding the seven bowls came and said to me, Come here. I will show you the judgment on the great harlot* who lives near the many waters.a
'These are the notes on that verse:
* (17:16) Babylon, the symbolic name (Rev 17:5) of Rome, is graphically described as the great harlot.
The Book of Revelations, or The Apocalypse, is generally understood to refer to Rome and the Roman Empire. Despite its weird language and imagery, the references are contemporary and contrast the ultimate dissolution of Rome and its empire with the message of life contained in the Gospels.
So, Rome is the great harlot and I'm guessing the many waters is the Mediterranean.
Here's a link to the NABRE. Most of the verses have explanatory notes.
http://www.usccb.org/bible/books-of-the-bible/index.cfm