The Spring and Autumn Period and the Warring States Period refer to the Bohai Sea.
After Qin and Han Dynasties, northern Cyprus was called Beihai.
Biography of Wu refers to Lake Baikal.
The classic refers to Lake Balkhash.
If it is the square sea of ancient sacrifices.
The North Sea and the West Sea don't exist at all.
In ancient times, China was surrounded by the sea.
In fact, at that time, only the East had a sea in China.
The territory of China has completely reached the South China Sea, long after the formation of the "Four Seas Theory". Before this, the "South China Sea" was also illusory.
As for Qinghai Lake in the West Sea and Lake Baikal in the North Sea. These two lakes are indeed called in history.
But China has never replaced the record of "four seas" with "two lakes".
The most typical example is the official sacrifice to the dragon gods of the four seas, the East China Sea sacrifice to Shandong, and the South China Sea sacrifice to Guangdong, while both the north and the west are "looking sacrifices", the north sacrifices to Hebei or Shanxi, and the west sacrifices to Gansu.