(Gladstone, OR)  --  Police say a 22-year-old Portland man drowned while swimming in the Clackamas River.  Authorities say the man was crossing the river with his cousin yesterday when he began to struggle and disappeared underwater.  The cousin tried unsuccessfully to reach the man, and rescue crews were able to pull the man from the water 15 minutes later.  The man, whose name hasn't been released, was pronounced dead at the scene.