The Ganges is probably a bad idea. The other two...why the heck not?
Ganges can be a good idea depending on location. For example, at its origin and part way through the plains, it is unbelievably pure and awesome.
Take a look: http://www.google.com/imgres?imgurl=http://www.grandcounter.com/images/800px-Bhagirathi_River_at_Gangotri.JPG&imgrefurl=http://www.grandcounter.com/&usg=__57A-JqBhyBOwuZYE_1eu1jB3jPE=&h=600&w=800&sz=129&hl=en&start=0&zoom=1&tbnid=1yn4oVqsWBIsNM:&tbnh=129&tbnw=152&ei=VmZ0TcqwE4L78AbNyLCFDw&prev=/images%3Fq%3Dganga%2Bat%2Bgangotri%26hl%3Den%26biw%3D1069%26bih%3D615%26gbv%3D2%26tbs%3Disch:1&itbs=1&iact=hc&vpx=767&vpy=123&dur=5608&hovh=194&hovw=259&tx=175&ty=126&oei=VmZ0TcqwE4L78AbNyLCFDw&page=1&ndsp=15&ved=1t:429,r:4,s:0
