The other issue beyond simply the pollution..We've had a lot of snow this year. A total of 69 inches in my area..last year we had major flooding with a total of 55 inches...
If we prematurely raise the level of the rivers...it will be ugly once the snow melts in the next few weeks. Which will of course cause a good amount of damage, as last years high rivers did not to mention even more pollution from broken pipes and sewer over flowing ...again
I personally think there are plenty of areas to put snow, but the water ways are the "easy" way out.