The Mythological Importance
The Yamuna and the Ganges or Ganga are considered to be the most sacred rivers in India. According to the legends, Yamuna was the daughter of 'Surya', the Sun God, and sister to 'Yama', the God of Death. Consequently, popular belief has it that those who take a dip in the holy waters of the source stream are not tormented by fears of death.
The main reason why it is so revered is that it flows through Vrindavan and Mathura, and is thus intimately connected to Lord Krishna's pastimes. As far as sanctity of river Yamuna is concerned, it is more directly connected with Lord Krishna than the Ganges. The Lord sanctified the River Yamuna from the beginning of his transcendental pastimes in the world. While his father 'Vasudeva' was crossing the Yamuna with baby Lord Krishna for a safe place at Gokul on the other bank of the river from Mathura, the Lord fell down in the river, and by the dust of his lotus feet the river at once became sanctified.
A bath in this river is said to be one hundred times more purifying than a bath in the Ganges. The reason being that even though the Ganges was once touched by the feet of Lord Vishnu, it was the Yamuna where Lord Krishna himself played and swam with his cowherd friends. He also sported in its waters with the beautiful 'gopis' of Brajbhoomi.
Popularly called Jamuna river in Uttar Pradesh state, northern India, rising in Himalayas near Yamunotri. It is about 234-km north of Haridwar. Technically the source of the Yamuna is Saptarishi Kund, a glacial lake. To reach it one has to climb from Yamunotri 12-km right up the mountain.
From Yamunotri the Yamuna flows south until it reaches Delhi. The river then flows towards Braj Mandala through Vrindavan and Mathura. From there, it goes through Agra and eventually merges with the Ganges and the underground Saraswati at Prayag in Allahabad. The Hindus consider this confluence of rivers a sacred place.