Rivers are rated for their difficulty on a scale of class 1  6.  A class 1 river has a slower moving current with little or no obstacles. Class 2 and 3 rivers generally are fast moving with some obstacles and smaller to medium size rapids. Class 4 rivers have long, continuous sections of white water and large waves which requires strong paddling and good teamwork in the boat. Class 5 rivers have powerful prolonged sections of rapids and big holes, which requires very strong paddling and preferably some previous rafting experience. Class 6 is considered to be almost impossible to run.