Why is river Ganga considered as sacred?

Ganga River is the most sacred river in Hindu religion. Ganga has been a symbol of divinity, spirituality, purity and moksha. Swami Vivekananda said, “Paris is the fountain-head of European civilization, as Gomukh is of the Ganga. Ganga finds mention in numerous ancient texts; she is a mother, a goddess, a life-giving river and a repository of people’s beliefs.

In Northern India, it is a major river on whose banks
The National River of India Ganga flows through India and Bangladesh
The river flows through the Himalayas, Gangetic plains and empties into the Bay of Bengal
In Indian traditions and culture, river Ganga is personified as Goddess Ganga
It is a revered belief that to remit sins, one has to take a dip in river Ganga. It further channelizes the salvation, so is believed in Indian culture

Many sacred places are located alongside the stretches of Ganga river:

Kali Ghat