This is very probably going to destroy the utility of Lake Powell for 10 years or more.
No it wont - the volume and limited data released on chemistry demonstrate that it will be so diluted by the time it flows into Powell as to be insignificant.
I AM NOT saying that it isn’t of major concern to those in the immediate vicinity (tens of miles) of the discharge; however three million gallons in the combined flow of the Animas/San Juan and Colorado is trivial.
Fish kills, wildlife impacts in the first few miles is very likely; regardless of the claims by the EPA toxicologist.
Does Vegas get its water supply from lake Powell?
D’oh! Lake Mead, not Powell.