尼亚加拉大瀑布的水是从哪里流过来的？

Where does the water come from?

• The Great Lakes is the world’s largest surface freshwater system in the world, about 18 percent of the world’s supply.
• The volume of water in the Great Lakes would cover North America in about 1 metre (3.5 ft.) of water.
• The water flows from streams and rivers that empty into the Great Lakes, from Lake Superior down through Niagara to Lake Ontario, then into the St. Lawrence River to the Atlantic Ocean. Water always flows down to the sea, and the land slopes downward through the Great Lakes Basin from west to east, but the Niagara River actually flows north.
• Today, less than one percent of the water of the Great Lakes is renewable on an annual basis (precipitation and groundwater). The rest is a legacy from the last ice age, or “fossil” water.
• There’s still water in the Great Lakes because they rely heavily on replenishment/renewal from precipitation (rain, sleet, snow, hail) and groundwater.
• The brown foam below Niagara Falls is a natural result of tons of water plummeting into the depths below. It is not dangerous. The brown colour is clay, which contains suspended particles of decayed vegetative matter. It is mostly from the shallow eastern basin of Lake Erie.