Other contributors have said "What about niagara falls?" is the same question as "What river is Niagara falls on?" If you believe that these are not asking the same thing and should be answered differently, click here
It is about 170ft deep just below the fall. That is the deepest section of the river. It is also about 125ft deep in the whirlpool, below the whirlpool rapids.
Neither. It is a waterfall on the Niagara River. Niagara Falls can also refer to two cities, one on each side of the waterfall itself and in different countries.