Yes, it is the second largest inhabited of the Channel Islands which also include Jersey, Alderney, Sark and Herm and the minor inhabited islands of Jethou, Brechou and Lihou.
The Channel Islands are Crown dependencies of Britain but are not actually part of the sovereign state of the United Kingdom.The Channel Island are not part of the EU.
The island of Guernsey has no recognisable rivers. There are however many local small streams, known as douits (pronounced dw-it-s). Most of these have no name of their own (as a river might have)....