Legend of Yamunotri
According to a legend, Sage Asit Muni had his hermitage here. Throughout his life he bathed daily in the waters of both Ganga and Yamuna. Gradually, unable to go to Gangotri during his old age, a stream of Ganga appeared opposite Yamunotri for him. Another legend says that Yamunas supposed frivolousness was due to her mothers inability to look at Yamunas father, Lord Surya, in the eye due to his tremendous radiance. It is also said that if one bathes in the waters of Yamuna, the person ceases to die a painful death since Yamuna is the sister of Yama, the lord of death.
According to Hindu mythology, Surya, the sun god is the father of Yamuna, and Yama, the god of death. It is said that since Yamuna is the sister of Yama, anyone who who bathes in the river is spared a painful death.