一衣带水 A thin strip of water
Explanation
这个成语形容两地相隔虽有江河湖海，但距离很近，不足以成为交往的阻碍。
This idiom describes two places that are separated by rivers, lakes, or seas, but are so close that the distance is not a barrier to communication.
Origin Story
公元581年，杨坚取代北周称帝，建立了隋朝，称隋文帝，统一北方后，面对长江以南的陈朝就想统一全国，他经常对手下人说：“我是老百姓的父母，难道因为像衣带似的长江就能挡住我去拯救那里的老百姓吗？”于是出兵渡江灭掉陈朝，最终完成了统一大业。
In 581 AD, Yang Jian overthrew the Northern Zhou Dynasty and established the Sui Dynasty, taking the title of Sui Wendi. After unifying the north, he looked towards the Chen Dynasty in the south of the Yangtze River and wanted to unify all of China. He often said to his subordinates: “I am the father of the people. Can a narrow waterway like the Yangtze River stop me from saving the people there?
Usage
这个成语一般用来形容两地之间距离很近，方便交流。
This idiom is generally used to describe two places that are very close to each other, making communication easy.
Examples
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两国人民一衣带水，唇亡齿寒，彼此之间有着密切的联系。
liang guo ren min yi yi dai shui, chun wang chi han, bi ci zhi jian you zhe mi qie de lian xi.
The two peoples are connected by a narrow strip of water, sharing a common destiny.
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虽然相隔千里，但我们之间的友谊却是一衣带水，永远不会断绝。
sui ran xiang ge qian li, dan wo men zhi jian de you yi que shi yi yi dai shui, yong yuan bu hui duan jue
Although we are thousands of miles apart, our friendship is a thin strip of water, never to be broken.