The speed of the Niagara River varies from location to location.

At the southern end of the river, water flows approximately 8 kilometres (5 miles) per hour as it passes under the Peace Bridge at Fort Erie. Just above the falls in the Upper Rapids the speed of the water can reach 68 kilometres (41 miles) per hour. The speed at the crest of the falls is 32 kilometres (20 miles) per hour (22 miles) per hour. The speed of the water at the crest of the falls is 32 kilometres (20 miles) per hour. The speed of the water in the lower Whirlpool Rapids below the falls is about 35.5 (22 miles) per hour. This is one of the wildest rapids in the world with a classification of V-V1.

I can vouch for this having lost a pair of glasses when going through these rapids on a zodiac in August 1975.It was the inaugural trip of a proposed thrill ride. Permission for future rides was never given after three people lost their lives a week later when thrown off the zodiacs into the Niagara River. I was one of the lucky ones to make the trip successfully.