How has the indian practice of cremating their dead been a problem for the river?

In January 2015 crows filled the sky and people walked up to find 100 plus corpses floating in a canal near the Ganges river. Those who've let their deceased

Loved ones go in the Ganges river (due to not affording it, can coast up to a third of their yearly wages) are hoping wild dogs get the bodies but when dogs don't come, they bodies rot ... thus polluting the river.