The story goes that Liu Bowen and Yao Guangxiao built the city of Beijing and discovered several "sea eyes" (underground waterways) in the city, with the eastern ones leading all the way to the sea. The two largest were one at Jade Spring Mountain in the west of Beijing, which was under a large temple, another in Beihai Park, which was sealed by the White Pagoda, and one at Beixin Bridge that had not been sealed. A sea beast would occasionally come out from this unsealed eye causing trouble. Liu Bowen then negotiated with the sea beast: “We need to build the city of Beijing, so you go down there and wait until the bridge changes from a new bridge to an old bridge, then you can come back out.” The sea beast thought about it and jumped into the sea eye. From then on, Liu Bowen told the people that this place could only be called "Beixin Bridge" and never "Old Bridge."
Later, the sea eye under Beixin Bridge was disturbed twice. The first time was when the Japanese invaded Beijing. They pulled a huge iron chain upwards and after a kilometer or two, they saw murky yellow water bubbling up below, accompanied by the sound of sea breeze and a fishy smell. The Japanese panicked and quickly let the chain fall back. The second time was during the Cultural Revolution when the Red Guards tried to pull the big iron chain upward as well. Just like the Japanese, they got scared and quickly restored everything back to its original state.