I can't find a reference, unfortunately. This was in the Arkansas River watershed, likely back in the 1990s, and so has likely not made it over the digital divide, yet. Consequently, we might only have my memory of the event to depend on. I will concede that it may have been local (Colorado) authorities, and not the US EPA.

But my point still stands: Drinking water is surprisingly and counterintuitively an environmental hazard. It is easy to conclude that the local environmental agency is being irrational without good science media explaining.

It is well-understood that chlorinated water causes fish kills:

  https://www.fws.gov/nc-es/edout/albefitfish1.html
  http://www.vita-d-chlor.com/specs/awwarfdechlorguides.htm
  http://www.fosc.org/AL-Chlorine.htm
  http://ntv.ca/chlorinated-water-killed-hundreds-of-fish-in-waterford-river/