Name: What’s so great about the Great Lakes? - Cheri Dobbs and Jennifer Gabrys
Uploaded: 2017-01-11T03:06:51.000Z
Duration: 4 min 52 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Adverbs of degree

are so massive  that they border eight states

and contain 23 quadrillion  liters of water.

That's enough to cover the land area of the contiguous United States

supporting a region that's home to over 3,500 species.

But how did such a vast and unique geological feature come to be?

The story begins near the end of the last ice age over 10,000 years ago,

and the glaciers that cloaked the Earth's surface began their slow retreat.

These immense ice sheets carved out a series of basins.

Those basins filled with water as the ice began to melt,

creating the world's largest area of freshwater lakes.

Over time, channels developed between these basins,

and water began to flow in  an ongoing exchange

In fact, today,  the interconnected Great Lakes

contain almost 20% of the world's supply of fresh surface water.

The water's journey begins in the far north of Lake Superior,

which is the deepest, coldest, and clearest of the lakes,

Lake Superior sinks to depths of 406 meters,

creating a unique and diverse ecosystem that includes more that 80 fish species.

A given drop of water spends on average 200 years in this lake

before flowing into Lake Michigan or Lake Huron.

Linked by the Straits of Mackinac, these two lakes are technically one.

the third largest of the lakes by surface area.

Water slowly moves through  its cul-de-sac shape

and encounters the world's largest freshwater dunes,

To the east is Lake Huron, which has the longest shoreline.

It's sparsely populated,  but heavily forested,

including 7,000-year-old petrified trees.

Below them, water continues to flow southeastwards

This lake's status as the warmest and shallowest of the five

has ensured an abundance of animal life, including millions of migrating birds.

Finally, the water reaches its last stop by dramatically plunging

more than 50 meters down the thundering Niagara Falls

into Lake Ontario, the smallest lake by surface area.

>From there, some of this well-traveled water enters the St. Lawrence River,

the perpetually flowing Great Lakes bring us multiple benefits.

By moving water across  more than 3,200 kilometers,

the Great Lakes also provide drinking water for upward of 40 million people

and 212 billion liters a day  for the industries and farms

But our dependence on the system is having a range of negative impacts, too.

The Great Lakes coastal habitats are being degraded and increasingly populated,

to industrial, urban, and agricultural pollutants.

Because less than 1% of the water leaves the Lake's system annually,

decades-old pollutants still lurk in its waters.

That creates dead zones in some regions where no plants or animals can survive.

Humans have also inadvertently introduced

more than 100 non-native and invasive species into the lakes,

such as zebra and quagga mussels, and sea lampreys

that have decimated some indigenous fish populations.

On a larger scale, climate change is causing the waters to warm,

thus reducing water levels and changing the distribution of aquatic life.

Luckily, in recent years, governments have started to recognize the immense value

Partnerships between the United States and Canada are underway to reduce pollution,

Protecting something as massive as the Great Lakes system

will require the collaboration  of many organizations,

if we can preserve the wonder  of this flowing inland sea.