You can't identify for me what makes this particular pipeline special compared to all the other ones.  You do know that we have oil pipelines snaked all throughout this country in many different states and countries, right?  What makes the environmental hazards of this one special?  Is this the first time we've built a pipeline near or under a river?  I don't think so.  

"The 1972 Clean Water Act makes it unlawful to discharge any pollutant from single identifiable source — such as a pipe — into certain bodies of water without a permit."

But it's not discharging oil INTO the water, it's being constructed UNDERNEATH the water.  This is not the first time a pipeline has crossed a river before, so I'm failing to make the connection between your claims and how they apply only to this specific pipeline.  

I think it really just comes down to the existence of protesters.  It follows the exact path of an existing pipeline which was never protested.