Your title yalu river is a Chinese accent for the Amnok River.
The Amnok River is a natural border dividing Manchuria with North Korea in a geographical sense and The River is not only our rivers, but also our rivers that are used and managed by China.
So, the Chinese characters on the Amnok River are used just like Korea or China. but It's just the difference that we pronounce "amnok" but the Chinese say "yalu."
But, the international designation of the Yalu River is because the people of the West saw the Yalu River 200 to 50 years ago through China first.
So, However, it is wrong to call the name of a nation's big river the wrong way around the world. Therefore, we insist on being called the Amnokgang, our official name.