No, it isn't, not by far. Victoria Falls in Africa (called Mosi-oa-Tunya or "the Smoke that Thunders" in the local tongue) is considered by many accounts the largest waterfall in the world based on sheer size (height and width combined). It's found on the Zambezi River between Zambia and Zimbabwe. It's twice as high as Niagara and around 500m wider. Iguazu Falls in Brazil is even wider still while being taller than Niagara. Niagara Falls is the most powerful falls in North America and its great claim to fame is its accessibility and great scenery,

No. Victoria Falls on the Zambezi river is the world's largest.