The Yue Bay was first settled by humans during or soon after the era of Raava. The local guardian spirit, Lady Tienhai, allowed humans to stay and protect them from harm, including from other spirits. Over millennia, the settlement grew into Tienhaishi, a powerful monarchy that had become the greatest city in the world by the lifetime of Avatar Yangchen. Around the lifetime of Yangchen, Lady Tienhai fell in love with the last king of Tienhaishi and took a mortal form to be with him. Then she eventually passed away, which enraged the powerful General Old Iron. Yangchen came to an agreement with the spirit that the city would be abandoned, and the bay was reclaimed by nature.
Shortly after the end of the Hundred Year War, Earth Kingdom and Fire Nation industrialists discovered that the bay was home to the largest crystal deposit in the world outside Ba Sing Se. The Earthen Fire Refinery was established in the area and a small industrial town started to spring up in the region. The area also began to become polluted by a nearby iron mine. In response, General Old Iron began to resurface and demanded that Avatar Aang destroy the human settlements. The spirit was defeated by the Avatar and retreated from the area, acknowledging defeat. Despite this, Aang sought to bring back spirituality to the area by celebrating the Spirits' Friendship Festival.
The urban settlement continued to grow rapidly into a small city known as Cranefish Town. With no official government in the area due to the ambiguous status of the nearby Fire Nation colonies, turf wars between bender gangs erupted on the streets and the social divide between benders and nonbenders began to widen. The Cranefish Town Business Council was established to oversee the laws of the town. After a bender supremacist uprising was foiled by Avatar Aang and his allies, they decided to stay in the town and help it prosper.
Eventually, the settlement was renamed Republic City, becoming the capital of a fifth nation, the United Republic of Nations, founded by Avatar Aang and Fire Lord Zuko. The body of water made Republic City easily accessible for trade by water, and it was instrumental in the growth of the city. The bay was home to several conflicts during the 170s AG, including the naval battle between the United Forces and the Equalists in the Battle for Republic City; the duel between Avatar Korra and Dark Avatar Unalaq during Harmonic Convergence, and the United Forces' battleships being destroyed by a spirit energy cannon during the invasion of the United Republic of Nations.
Yue Bay leads inland toward Republic City, directly connecting to numerous areas and districts within the mainland. Within its waters are several small islands on which landmarks have been established. In addition to this, several large suspension bridges connect the city center to outlying districts at many points.
Air Temple Island
- Main article: Air Temple Island
Located in Yue Bay, Air Temple Island is the home of Tenzin and his family, and is therefore the residence of one of the most powerful governing figures of Republic City. The temple was originally built by Avatar Aang himself. Air Temple Island was also home to the young Avatar-in-training, Korra, and the Air Acolytes, as well as becoming home to the new airbenders that arose after Harmonic Convergence.
- Main article: Pro-bending Arena
Official pro-bending matches are held in Republic City's Pro-bending Arena, a large glass-domed structure located at the end of a pier that extends into Yue Bay. As a testament to the sport's popularity, the arena's exterior has a golden appearance and is lit at night, making it a prominent city landmark.
Aang Memorial Island
- Main article: Aang Memorial Island
Aang Memorial Island features a massive sculpture of Avatar Aang commissioned by the Fire Nation some years after the end of the Hundred Year War for display in Republic City. It stands as a symbol of peace and goodwill.