Niagara Falls FAQ: The Niagara River

The deepest spot in the Niagara River is just below the Horseshoe Falls.

Here the water is roughly 170 ft (52 m) deep. The erosion from the tumbling water has gouged into the river bed, creating a depression almost as deep as the falls are tall. Under the American Falls, piles of rock debris keep the immediate area shallow.

The Niagara Whirlpool formed nearly 4,200 years ago when the erosion and recession of Niagara Falls, which up to this point was a sluggish process, reached a soft spot in the landscape. Saint David’s Buried Gorge was an ancient, pre-glacial river valley filled in with soft glacial silt and stone. When Niagara Falls eroded its way into this hidden gorge, it rapidly began washing away the gorge’s soft filling. It is speculated that when the Falls hit the buried gorge, it was just a matter of weeks, perhaps even days of violent erosion while it carved out the Whirlpool basin. It was a swift and powerful geological event considering the Falls had taken nearly 8000 years to get to this point.

Saint David’s Buried Gorge ran perpendicular to the current path of the Fall’s erosion, and resulted in a 90 degree turn in the river. Just upstream the narrow Niagara Gorge at the Whirlpool rapids sends water jetting into the Whirlpool basin. It hits the solid rock basin across the Whirlpool at Niagara Glen. Thousand of years of these forces has resulted in a dimpling of the basin; giving it an oval shape that juts past the turn in the river.

It depends on the time of day.

When the Niagara River is at full flow the Whirlpool will flow in a counterclockwise direction. When the river flow drops, usually when more flow is diverted to the power plants, the flow of the whirlpool reverses (clockwise). This usually happens during the tourist off-season (November 1 through April 1).

Just upstream from the Whirlpool is the narrowest section of the Niagara: the Eddy Basin. This pinch in the gorge is not sufficient for the normal flow of the river to pass through, so some of the water is pushed backward. The water at the shore actually flows backward at this location.

The Niagara River reaches depths of 125 ft (38 m) as it passes through the Niagara Whirlpool.

For more information on the Niagara Whirlpool, visit our Niagara Whirlpool State Park page.

Specific sections of the Niagara River are classified differently. First let’s review what the classes stand for. Whitewater rapids are graded on the International Scale of River Difficulty, which has 6 “Classes.”

• Class I: Easy. Waves small; passages clear; no serious obstacles.

• Class II: Medium. Rapids of moderate difficulty with passages clear. Requires experience plus suitable outfit and boat.

• Class III: Difficult. Waves numerous, high, irregular; rocks; eddies; rapids with narrow passages, requiring expertise in maneuvering; scouting usually needed. Requires good operator and boat.

• Class IV: Very difficult. Long rapids; waves high, irregular; dangerous rocks; boiling eddies; best passages difficult to scout; scouting mandatory first time; powerful and precise maneuvering required. Demands expert boatman and excellent boat and good quality equipment.

• Class V: Extremely Difficult. Exceedingly difficult, long and violent rapids, following each other almost without interruption; riverbed extremely obstructed; big drops; violent current; very steep gradient; close study essential but often difficult. Requires best person, boat, and outfit suited to the situation. All possible precautions must be taken.

• Class VI: Unrunnable. Chances are: you’re going to die on this.

Most of the Niagara River’s waters are graded as Class I.This includes the run from Lake Erie up to the Cascade Rapids just above the falls. Here the water’s classification is up for debate. Although the whitewater is runnable (probably a Class IV), that would mean ending up over the falls at the end. The Falls themselves and the immediate area below are certainly a Class VI: unrunnable.

The navigable portions of the Upper Great Gorge (below the Falls, where the Maid of the Mist boats run) are roughly a Class IV. Although the water here lacks free-standing waves and obvious obstacles, the whirlpool currents can trap small craft and push them towards the rocky cliff or into the downpour of the falls. In addition, high quantities of bubbles rising from below can cause buoyancy problems for personal craft.

Heading downriver from the basin of the Falls, the gorge remains wide and the water calms, eventually decreasing to a Class I. At the Whirlpool Rapids Bridge the gorge suddenly narrows by more than half and water speeds up to approximately 22 mph (35 kmph) forming the world famous Whirlpool Rapids. Here the large volume of the Niagara is forced through a basin unable to fully support its bulk, forming violent currents and standing waves reaching 15 ft high. The rapids shoot out of the narrow gorge and into the swirling Niagara Whirlpool. Here craft would need to fight the powerful current to navigate the 90 degree bend in the river, in order to escape the rapids. The Whirlpool Rapids run is easily a Class V and at times of higher flow, un-runnable.

Just past the Whirlpool, the gorge widens and the river slows for a short bit, until it reaches Devil’s Hole at the Lower Great Gorge. Again, a constriction of the gorge basin speeds up and agitates the Niagara; forming the Lower Whirlpool Rapids. Not nearly as violent as upriver, the water here reaches a Class III.

After Devils Hole, the river calms and it is smooth sailing all the way north to Lake Ontario.

The Niagara River Gorge’s massive cliffs reach maximum height at the escarpment itself near Queenston, ON. Here the Gorge walls are nearly 322 ft (98 m) high. The height of the cliffs decline as you move further south, eventually reaching their lowest height at Niagara Falls.