According to the legend, it is believed that the Maga Purohits, now known as Shakya Dwipi Brahmins who had an expertise in Sun worshiping were called by the local kings for the same and so the tradition of Chhath Pooja was started. The areas where the Shakya Dwipi Brahmins are found, celebrates Chhath with great zeal.
Some believe that the Chhath Pooja has been there from the time of ancient Vedas text as in the Rig Veda, also there are hymns in which Sun God is worshiped and similar rituals are followed. It even has links with the Sanskrit written book, Mahabharata which has a character named Draupadi who is doing similar practices. In the text, Pandavas, the ruler of Hastinapur along with their wife Draupadi had performed the rituals of the Chhath as adviced by Dhaumya, the noble sage. By performing these rituals, Draupadi was able to solve her problem and the Pandavas also got their lost kingdom with the help of that.
Another belief says that the Chhath Pooja was initiated by Karna, son of the surya. He reigned over the Anga Desh, the Bhagalpur District in Bihar during the Mahabharata times. He was a great warrior and fought really hard.
The saints of Yore used the Chhath Pooja method to avoid food for energy. They believed that they go with the energy from the Sun. So, for that, they used the Chhath Pooja method. Chhath is a very popular festival in Darbhanga, Muzzaffarpur, Samastipur and other areas of Bihar and Jharkhand. It is being celebrated in all parts of our country including the states in the south like Mangalore, Karnataka etc. Chhath Pooja is celebrated on the Panambur Beach in Bihar and Jharkhand.