Swimming the Allegheny River. The Allegheny River is a beautiful river set in the heart of the Allegheny Mountains. When I was a kid we would go camping at a camp site in the Allegheny forest. My uncle would run his boat. We would swim in the river almost all day long. From one side to the other side, it was approximately 1 1/2 miles wide. We would cross the river by swimming. At least three times a day. So we swam the Allegheny River every year for about ten year. Allegheny River in the heart of Pennsylvania a river of fun.