What's so great about the Great Lakes?
是什么让五大湖如此伟大？
They're known as America's inland seas.
它也被称作美国的内海。
The North American Great Lakes Huron, Ontario, Michigan, Erie, and Superior
北美五大湖，休伦湖，安大略湖，密歇根湖，伊利湖以及苏必利尔湖，
are so massive that they border eight states and contain 23 quadrillion liters of water.
它们非常宏大，构成八个州的边界，包含23千万亿公升水。
That's enough to cover the land area of the contiguous United States three meters deep.
即使将美国国土全部覆盖，水位仍可达三米深。
These vast bodies of water span forest, grassland, and wetland habitats,
这片广阔的水域跨越森林、草原和湿地生态系统，
supporting a region that's home to over 3,500 species.
供养着超过3500种生物。
But how did such a vast and unique geological feature come to be?
但是，这片广阔而独特的地质特征是如何形成的呢？
The story begins near the end of the last ice age over 10,000 years ago,
故事要从上个冰河世纪的末期说起，也就是超过1万年以前，
a time when the climate was warming and the glaciers that cloaked the Earth's surface began their slow retreat.
气候转暖，地球表面的冰川缓缓融化。
These immense ice sheets carved out a series of basins.
无垠冰川曾雕刻出形态各异的盆地。
Those basins filled with water as the ice began to melt, creating the world's largest area of freshwater lakes.
冰雪融化后，雪水流入盆地，创造出了世界上最大的淡水湖。
Over time, channels developed between these basins, and water began to flow in an ongoing exchange that persists to this day.
不久，盆地间的河道凸显，湖水流入并相互交融一直到今日。
In fact, today, the interconnected Great Lakes contain almost 20% of the world's supply of fresh surface water.
事实上，今天，这些相互交融的五大湖，包含了几乎世界上20%的淡水供应。
The water's journey begins in the far north of Lake Superior,
水的旅程起始于最北部的苏必利尔湖，
which is the deepest, coldest, and clearest of the lakes, containing half the system's water.
也是最深、最冷、最干净的湖，包含了整个五大湖系统一半的水。
Lake Superior sinks to depths of 406 meters, creating a unique and diverse ecosystem that includes more that 80 fish species.
苏必利尔湖最深处可达406米，创造了独一无二的多样的生态系统，包含80多种鱼。
A given drop of water spends on average 200 years in this lake before flowing into Lake Michigan or Lake Huron.
一滴水平均需要200年才能从这里流入密歇根湖或休伦湖。
Linked by the Straits of Mackinac, these two lakes are technically one.
在麦基诺海峡的连接下，这两大湖实际是一体的。
To the west lies Lake Michigan, the third largest of the lakes by surface area.
西边是密歇根湖，水域面积世界第三。

Water slowly moves through its cul-de-sac shape and encounters the world's largest freshwater dunes,
水沿着“死胡同”缓缓流回，沿途经过世界最大的淡水滩，
many wildlife species, and unique fossilized coral.
那里有数不清的野生物种和独特的珊瑚化石。
To the east is Lake Huron, which has the longest shoreline.
东边是享有最长海岸线的休伦湖。
It's sparsely populated, but heavily forested, including 7,000-year-old petrified trees.
那里人口稀少，植被丰富，7000年的石化树也长于此地。
Below them, water continues to flow southeastwards from Lake Huron into Lake Erie.
植被下，湖水沿东南继续流淌，流出休伦湖便进入伊利湖。
This lake's status as the warmest and shallowest of the five
作为五大湖中最温暖、也是最浅的地方，
has ensured an abundance of animal life, including millions of migrating birds.
这里物种丰富，上百万候鸟迁徙来此。
Finally, the water reaches its last stop
最后，水流至最后一站，
by dramatically plunging more than 50 meters down the thundering Niagara Falls into Lake Ontario, the smallest lake by surface area.
来到振聋发聩的尼亚加拉瀑布，经过超过50米的猛烈下冲，进入表面积最小的湖安大略湖。
From there, some of this well-traveled water enters the St. Lawrence River, eventually reaching the Atlantic Ocean.
至此，这滴水经历漫长旅程，流入圣劳伦斯河，并最终汇入大西洋。
In addition to being a natural wonder, the perpetually flowing Great Lakes bring us multiple benefits.
除了作为自然景观，五大湖日复一日流动着，为人类带来不少福利。
They provide natural water filtration, flood control, and nutrients cycling.
它们提供了天然水过滤、洪水控制以及营养循环。
By moving water across more than 3,200 kilometers,
随着湖水超过3200千米的移动，
the Great Lakes also provide drinking water for upward of 40 million people
五大湖也给上游4千万居民提供了饮用水，
and 212 billion liters a day for the industries and farms that line their banks.
给沿岸的工厂和农庄每天带来2120亿公升水。
But our dependence on the system is having a range of negative impacts, too.
但是，我们对五大湖的依赖也造成了一系列负面效果。
The Great Lakes coastal habitats are being degraded and increasingly populated,
五大湖沿岸生态栖息地逐渐退化，被越来越多的人口侵蚀，
exposing the once pristine waters to industrial, urban, and agricultural pollutants.
曾经原生态的水域暴露给工厂、城市和农业的污染物。
Because less than 1% of the water leaves the Lake's system annually, decades-old pollutants still lurk in its waters.
由于每年仅有1%的水能离开这个系统，数十年的旧物染污仍然会逗留在水域中。
Humans have also inadvertently introduced more than 100 non-native and invasive species into the lakes,
人类也无意间向湖中引进了超过100种非原生的入侵物种，
such as zebra and quagga mussels, and sea lampreys that have decimated some indigenous fish populations.
例如两种斑纹贝和七鳃鳗，它们已经使一些土著鱼类灭绝。
On a larger scale, climate change is causing the waters to warm,
更大程度上讲，气候的变化让这里的水越来越温暖，
thus reducing water levels and changing the distribution of aquatic life.
使水位下降，造成水生物分布的改变。
Luckily, in recent years, governments have started to recognize the immense value of this natural resource.
幸运的是，近几年，政府部门开始意识到这项自然资源的巨大价值。
Partnerships between the United States and Canada are underway to reduce pollution,
美国和加拿大开始联手治理污染，
protect coastal habitats, and halt the spread of invasive species.
保护生态栖息地，并阻止入侵物种的扩散。
Protecting something as massive as the Great Lakes system will require the collaboration of many organizations,
保护像五大湖这么大的生态系统，需要许多组织的合作参与，
but the effort is critical if we can preserve the wonder of this flowing inland sea.
但是要想保住这个流动着的内陆奇迹，这项工作势在必行。