Just upstream from the falls' current location, Goat Island splits the course of the Niagara River, resulting in the separation of Horseshoe Falls to the west from the American and Bridal Veil Falls to the east. Engineering has slowed erosion and recession.

Niagara Falls is split into three distinct sections primarily due to the geological presence of Goat Island and Luna Island, which act as natural dividers for the massive flow of the Niagara River. As the river moves north from Lake Erie toward Lake Ontario, it encounters Goat Island, which forces the water to divert in two main directions. The vast majority of the water (about 90%) is diverted over the crest of the Horseshoe Falls on the Canadian side, creating the iconic curved shape. The remaining 10% flows around the other side of Goat Island, forming the American Falls. A smaller diversion created by the tiny Luna Island separates a portion of the American flow into the Bridal Veil Falls. Over the last 12,000 years, the falls have actually receded about 7 miles upstream due to erosion; as they moved, they hit these limestone and shale rock formations that were more resistant to the water's force, creating the multi-part spectacle we see today. Without these islands, Niagara would likely be one single, massive, and straight curtain of water rather than the tiered and uniquely shaped triple-waterfall system that exists now.