The deepest section in the Niagara River is just below the falls. It is so deep that it equals the height of the falls above: 52 metres (170 ft.) The Upper Niagara River extends 35 kilometres (22 mi.) from Lake Erie to the Cascade Rapids, which begin 1 kilometre (0.6 mi.)

The depth of the water at the base of Niagara Falls, specifically within the "Maid of the Mist" pool at the foot of the Horseshoe Falls, is surprisingly deep—often estimated to be around 170 feet (52 meters). This depth is almost equal to the height of the falls themselves. This massive underwater basin, known as a "plunge pool," was carved out over thousands of years by the sheer force of the water crashing down, combined with the abrasive power of rocks and debris being swirled around in the turbulent currents. The intense pressure and volume of the falling water (roughly 600,000 gallons per second during peak hours) create a constant scouring effect on the riverbed. Interestingly, while the water is extremely deep directly under the falls, the river eventually shallows out as it moves downstream toward the Niagara Gorge. Navigating these waters requires specialized vessels due to the extreme turbulence, mist, and the immense power generated by the descent of the upper Niagara River into the lower basin.