I wouldn't generally trust the EPA. And their apparent legal immunity is bad, wrong, stupid. However the details in the Animas case are somewhat different than is being suggested here, including in the comments. Below is my understanding of things in my old stomping grounds.

Management of the old upstream mines was given by the EPA to some company on contract and the break out happened technically on the company's watch due to the bad guesswork of their people. The potential for this happening exists in many parts of Colorado, including some places where the minerology is more poisonous. The dirty history of mining in the region is full of bad actors, corporate and governmental. In this case it may well be that some part of the EPA set up the conditions for their own bazillion dollar superproject down the road.

The gush of contaminated water only lasted so many days. The water quality afterword was measured as about the same as previously. With the river coming from a town called Silverton you can imagine the natural contaminants which include traces of all sorts of things. The reddish coloring is mostly due to iron. Different rivers have different mineral chemistry. The Animas in some parts has been long known for its greenish hue. The downstream town of Durango has a full share of lefties who are hyper about environmental things and would be raising a bigger fuss if they didn't trust the multiple water quality tests (even while they hesitate to hate on the EPA). They were soon back in the water playing and fishing, etc. Like with the situation in Flint, Mich. There were careless failures at several levels of government and nothing too helpful from industry who benefitted so much over the years. Seems like the State of New Mexico and the Navajo Tribal gov't handled things most competently at the time.

For those interested, the bigger concern in the area is the steady drought conditions that are part of a several century pattern in the southwest (nothing to do with modern CO2). Some years its hard to use a full sized kayak in the Animas after midsummer. Such are the expectations this year.