Yamuna is a sacred river for Hinduism. And is the main tributary for the Ganges River. She is also been worshipped as a Hindu Goddess. Yamuna is also know as yami in early literature and in later literature she is been called as kalindi. 

Yamuna is said to the daughter of Surya(THE SUN GOD) and Sanjana(THE CLOUD GODDESS). Making her the twin sister of Yama(GOD OF DEATH). 

Acc. To hindu scriptures, bathing in or drinking yamuna’s water removes sin. (The next time when u feel like a sinner. You know what to do 😂) While yama is depicted as the Lord of Death, Yami is said to be the Lady of Life. Yami is also addressed is hymn of yama in Rig Veda. Describing various drinks offered to dying sacrifices in the after life. 

Acc. To the Brahmana text Maitrayani Samhita narrates:

Yami grieved instantly to the death of Yama ( The first mortal to die). As there was continously day time at the start of creation. Yami was unable to understand the lapse of time, since yama’s death. 

The God created night seperating two days so that yami understood that time was passing and slowly recovered from her sorrow. ( probably that how the saying of time heals. Come into play😅) . 

She was also know as kalindi as Lord Krishna killed the Kalya nag in her. Due to which she turned black. There is another myth saying that Lord Shiva’s overflowing sexual desires for sati he made his way into The Yamuna. By doing so it turned the water black. That how she is said to get her name kalindi. Also, afterwards she being married to Lord Krishna as her wife Kalindi.