I like your comparison to the Ganges River. Here's a neat description of it:
"However, industry is not the only source of pollution [in the river Ganga]. Sheer volume of waste - estimated at nearly 1 billion litres per day - of mostly untreated raw sewage - is a significant factor. Also, inadequate cremation procedures contributes to a large number of partially burnt or unburnt corpses floating down the Ganga"
from http://www.cs.albany.edu/~amit/ganges.html
To make your story more impressive and (ahem) more scientifically sophisticated, you could refer to the principle of mass conservation for fluids: Area*velocity=k.
Excellent story overall. Since you've taken the time & effort to craft it, why not send it off w/ your secondary. It would be a waste to not use such beautiful prose