The left wants an unfettered flow of people who will come to the US and do this to our lakes and rivers. And this is far worse than global warming.
Bring in a few high temp furnaces. Start on one end and grab all that sewage and move it to the furnaces. Burn at high temps so there is little pollution released.
Wash, rinse and repeat until cleaned up. As far as turning that mess into clean water, let the scientists deal with that one.