The water travels at different speeds along the length of the Niagara River. South of the Falls where the river is wide and slow, the maximum speed is about 40 km/h. Near the brink of the Falls, a speed of 109 km/h has been recorded. As the water travels through the Whirlpool Rapids at White Water Walk, it is traveling at about 48km/hr or 30mph, creating the Whirlpool Rapids - "Class 6 white-water rapids".
Rivers are rated on a scale of 1 to 6 in eastern North America, and 1 to 10 in western North America. The Colorado River is the benchmark for white-water, where some sections are Class 5 and 6 and the flow is 60,000cfs.