The EPA Caused a Huge Toxic Spill Now Streaming Toward Lake Powell

"A toxic plume of one million gallons of untreated wastewater accidentally released by U.S. Environmental Protection Agency (EPA) workers from a closed mine upriver in Silverton, Colorado last Wednesday is to blame for the Animas’ dramatically different hue from its normal color."

So, EPA workers released the wastewater. It was an accident, so presumably the water wouldn't have been released if the EPA workers had done something differently (or not done anything at all). Thus, why is it inaccurate to say that the problem was caused by the EPA?

"Generally isn't it their job to protect the environment?"

Yes, but that doesn't mean that they can't do harm to the environment when they screw up.