Well at least you know it is probably not a good place to go swimming unless you need some bloodletting done.
I still wonder if the reason there are no fish is because none were ever stocked? It may have been built as a public service for the local livestock producers as a watering hole? Or even as a communal project by ranchers??? Just some guesses.
The water Ph level looks acceptable.
Mexico City is down in a hole so you must be at some elevation. Do you know the approximate elevation of the pond?
I can see why you want to get out of the city is that is where you work. Been there a couple of times and that was more than enough. Way too many people for a country boy.
