Ques again!

Hi, I have asked this question before but didn't get a detailed answer. How is Vishnuji and ramji related to Ganga. I learned that it is said that ganga is known as vishnupadi but I would really want to know the whole story.also usually I have heard ganga being referred to ramji ki ganga so whats the story behind that. I would be really grateful if you could answer this question.

Thanks a lot.