Got this amazing picture from http://www.krishna.se/Art/ganga_descent.html. Can’t praise the artist enough! What a beauty this pic is!
The painting shows an artist’s rendition of how Ganga, when She deigned to come down to Earth from Heaven, was received by Lord Shiva. The story of Bhagiratha’s penances and the famous phrase Bhagiratha Prayatnam are wonderful to read about. Shiva is said to have locked up the arrogant Ganga in his locks, until further prayers and penance from Bhagiratha would see her through, but not before further being consumed (and then released, once again on Bhagiratha’s prayers) by the rishi Jahnu, which earned Her the appellation Jaahnavi.
Also see the wikipedia entry on Ganga.